Systems and methods for high-altitude radio/optical hybrid platform

ABSTRACT

Techniques for data transmission including receiving, at a geostationary earth orbiting satellite, forward-direction user data via a forward optical link; transmitting, by the geostationary earth orbiting satellite via multiple radio frequency (RF) spot beams, the forward-direction user data received via the forward optical link; receiving, at a stratospheric high-altitude communication device, forward-direction user data via multiple concurrent forward RF feeder links; transmitting, by the stratospheric high-altitude communication device via the forward optical link, the forward-direction user data received via the forward RF feeder links; transmitting, by each of multiple ground-based feeder RF terminals at a same RF feeder site, a respective one of the forward RF feeder links. At least 95% of forward feeder data throughput for all of the forward RF service link transmissions by the satellite is carried via the forward optical link and the forward RF feeder links.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims a benefit of priority to U.S. Provisional PatentApplication No. 62/745,254, filed on Oct. 12, 2018 (entitled “HighAltitude Radio/Optical Hybrid Platform and Diversity Optical LinkPlatform”), which is incorporated by reference herein in its entirety.

BACKGROUND

Individual high-throughput satellites in geosynchronous earth orbit(GEO) over time offer increasing aggregate end-user data throughput. Forexample, the EchoStar 19 satellite, launched in 2016, offers a datathroughput in excess of 200 gigabits per second (Gbps). One limit toachieving terabit per second (Tbps) forward data throughput (alsoreferred to as “data capacity” or “capacity”) from a single GEOsatellite is available forward feeder link bandwidth for delivering datato the satellite. With radio frequency (RF) communications, includingvarious “millimeter wave” bands, such rates are generally impracticaland expensive. RF feeder links must comply with regulatory constraintsand also not conflict with user RF links (the co-siting problem), whichmakes the following RF bands undesirable:

-   -   27.5-28.35 GHz has geographical limitations due to conflicts        with 5G cellular communications technology efforts.    -   28.6-29.1 GHz is utilized by NGSO (non-geostationary orbit)        communication satellites, placing the band at risk from various        LEO satellite constellation plans.    -   License-exempt V-band (50-75 GHz) guarantees 4 GHz of bandwidth,        with a likely additional 2 GHz, another 2 GHz hopeful, and        another 2 GHz in the distant future.

Plus, at this time, the W-band (75-110 GHz), although it offers 10 GHz,requires further technical development for this purpose for use in GEORF feeder links. Additionally, even with a spectral efficiency of 2.5bps/Hz, 400 GHz of total RF bandwidth is required to reach 1 Tbps datacapacity, so combined use of the available bands would require about 19gateways (GWs), plus many additional gateways for diversity. For GEOsatellites with data throughput in only a few hundreds of gigabits persecond, ground segment costs (construction, operation, and maintenance)for feeder links are already a significant percentage of overall networksystem cost. For 1 Tbps or greater data throughput, and the resultingincrease in the number of gateways, ground segment costs become evenmore significant. Also, although it may be possible to fit the needednumber of gateways in the United States, a very favorable satellitelocation would still be needed. Thus, in view of significant technologychallenges and regulatory uncertainty, use of RF feeders between theEarth's surface and a GEO satellite to achieve terabit per second orhigher data throughput is a difficult, uncertain, and expensivearchitecture.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations in accord withthe present teachings, by way of example only, not by way of limitation.In the figures, like reference numerals refer to the same or similarelements.

FIG. 1 illustrates an example satellite-based data telecommunicationsystem configured to utilize multiple RF feeder links between a compactfeeder RF terminal (RFT) array and a stratospheric high-altitudeplatform (HAP), a high capacity free space optical (FSO) feeder linkbetween the HAP and a space satellite, and RF service links between thespace satellite and a plurality of end user service RF terminals (RFTs).

FIG. 2A illustrates a plan view of an example of the feeder RFT arrayshown in FIG. 1.

FIG. 2B illustrates an alternative compact arrangement of the 40 feederRFTs shown in FIG. 2A, with the RFT cells arranged hexagonally.

FIG. 2C illustrates an example of the feeder RFT array with 61 feederRFTs.

FIG. 2D illustrates an example of the feeder RFT array with 79 feederRFTs.

FIG. 3 illustrates further details of the payload of the HAP shown inFIG. 1 and examples of operations performed by the payload in connectionwith the RF feeder links and the optical feeder link.

FIG. 4 illustrates further details of the satellite shown in FIG. 1 andexamples of operations performed by the satellite in connection with theoptical feeder link with the HAP 140 and the RF service links with enduser RFTs.

FIG. 5 illustrates an example of generating from network data a forwardRF feeder link included in a high capacity set of forward RF feederlinks, as may be performed under control of, and performed at least inpart by, the HAP data center shown in FIGS. 1 and 2A.

FIG. 6 illustrates an example of generating, at the HAP, the forwardoptical feeder link from the high capacity set of RF feeder linksreceived from the feeder RFT array, including, for example, the forwardRF feeder link shown in FIG. 5.

FIG. 7 illustrates an example of the satellite shown in FIGS. 1 and 4converting the forward optical feeder link received from the HAP intocorresponding RF service links for multiple spot beams.

FIGS. 8-10 illustrate examples of station-keeping and handoveroperations performed among a plurality of HAPs being operated as part ofa telecommunication system, as described for the HAP in FIGS. 1, 3, 5,and 6. In FIG. 8, a first HAP payload and a second HAP payload areoperating at approximately a first altitude in proximity to the feederRFT array at respective zenith distances relative to the feeder RFTarray. FIG. 9 illustrates an example in which a handover operation isperformed from the first HAP payload to the second HAP payload. FIG. 10illustrates an example arrangement of a fleet of three HAP payloadsafter the handover described in FIG. 9. FIG. 10 illustrates an examplearrangement of the fleet of three HAP payloads after FIG. 9.

FIGS. 11A-D illustrate examples in which RF feeder links are operatedwith degradation in capacity in accordance with a zenith distance andazimuth of a HAP relative to a feeder RFT array. In FIG. 11A, the HAP isat a zenith distance similar to the zenith distance shown for the firstHAP payload in FIG. 8. In FIG. 11B, the HAP has moved to a position withan increased zenith distance, and in response a total of 13 of thefeeder RFTs have been disabled. In FIG. 11C, the HAP has advanced toanother position to a further increased zenith distance, and in responsea total of 28 of the feeder RFTs have been disabled. In FIG. 11D, theHAP as advanced to another position, with a zenith distance similar tothe zenith distance in FIG. 11C, but at a much different azimuth.

FIGS. 12A and 12B show other approaches in which degraded capacity canbe provided between a HAP and a feeder RFT array, but in which otherHAPs pick up the remaining capacity.

FIG. 13 is a block diagram illustrating an example softwarearchitecture, various portions of which may be used in conjunction withvarious hardware architectures herein described, which may implement anyof the described features.

FIG. 14 is a block diagram illustrating components of an example machineconfigured to read instructions from a machine-readable medium andperform any of the described features.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. However, it should be apparent that the presentteachings may be practiced without such details. In other instances,well known methods, procedures, components, and/or circuitry have beendescribed at a relatively high-level, without detail, in order to avoidunnecessarily obscuring aspects of the present teachings. To moreclearly describe the disclosed subject matter, various featuresillustrated in the figures are not illustrated to scale, includingdistances or angles.

FIG. 1 illustrates an example satellite-based data telecommunicationsystem 100 (which may be referred to as a “communication system”)configured to utilize multiple RF feeder links between a compact feederRF terminal (RFT) array 128 and a stratospheric high-altitude platform(HAP) 140, a high capacity free space optical (FSO) feeder link 150between the HAP 140 and a space satellite 160, and RF service links 170between the space satellite 160 and a plurality of end user service RFterminals (RFTs) 112 (for example, the illustrated ground-based RFTs 112ba and 112 bb and air-based RFT 112 cd). In some implementations, asillustrated in examples described below, at least 90% (including in someimplementations at least 95% or in some implementations at least 99%) offeeder data throughput (in the forward and/or reverse directions) forall of the RF service links 170 operated by a single GEO satellite 160(including all forward RF service link signals transmitted by thesatellite 160 and/or reverse RF service link signals received by thesatellite 160) is carried via a single optical feeder link 150 with asingle HAP 140 (noting that handoff operations may be performed tochange from operating the optical link 150 with a first HAP 140 to adifferent second HAP 140) and corresponding RF feeder links 130 betweenthe single HAP 140 and a single feeder RFT array 128 at a single RFfeeder site 129. For example, the single compact feeder RFT array 128,the single HAP 140, the single satellite 160 can operate together toprovide a total forward data capacity of 1 Tbps or greater to aplurality of service RFTs 112 configured to communicate via the RFservice links 170 with the satellite 160.

The telecommunication system 100 includes a gateway system 120 (whichmay be simply referred to as a “gateway”) configured to provide thetelecommunication system 100 with access to a public data communicationnetwork 122 (for example, the Internet) and/or a private datacommunication network 124, whereby the gateway 120 can receive datafrom, and send data via, the networks 122 and/or 124. In someimplementations, the gateway 120 is configured to perform quality ofservice (QoS) and/or caching functions to improve performance of thetelecommunication system 100. In some implementations, the gateway 120and/or other systems managed by a network operator are configured tocontrol operation of other aspects of the telecommunication system 100,such as HAP 140 and/or satellite 160. For example, the gateway 120 maybe configured to determine how upstream data is distributed via spotbeams 172 (which collectively refers to the spot beam transmissions bythe satellite 160, such as spot beams 172 a, 172 b, and 172 c shown inFIG. 1). In the example illustrated in FIG. 1, the gateway 120 isconfigured to send data to, and receive data from, participating serviceRFTs 112 via a HAP data center 126.

The HAP data center 126 is configured to utilize the feeder RFT array128, HAP 140, and satellite 160 to exchange data with the service RFTs112, with the feeder RFT array 128 and HAP 140 each serving as endpointsfor a plurality of RF feeder links 130. For providing forward-directeduser data received as network data from the gateway 120 as forward linkdata (encoding the forward-directed user data) to the satellite 160 fordistribution to the service RFTs 112, the HAP data center 126multiplexes, modulates, and encodes data for the spot beams 172 for RFtransmission by the feeder RFT array 128. The feeder RFT array 128includes a compact arrangement of a plurality of ground-based feederRFTs. For each of a plurality of active HAP-directed RFTs, a respectiveone of a plurality of RF feeder links 130 (including, in this example,an RF feeder link 310 b) each including a respective forward RF feederlink signal (which may be referred to as a “forward RF feeder link” oran “RF feeder uplink”) transmitted to the HAP 140. In this particularexample, the feeder RFT array 128 includes at least 40 activelyoperating feeder RFTs concurrently transmitting respective forward RFfeeder links. Each of the forward RF feeder links is transmitted at afrequency of at least 60 GHz (in some examples, at least 80 GHz) and hasa bandwidth of 10 GHz (5 GHz with right-hand circular polarization(RHCP) and 5 GHz with left-hand circular polarization (LHCP)), providinga total forward RF feeder link bandwidth of 400 GHz from the feeder RFTarray 128 to the HAP 140. With an average forward link MODCOD providinga spectral efficiency of 2.5 bps/Hz, a total forward data capacity of atleast 1 Tbps may be provided by the feeder RFT array 128. In otherexamples, different values may be used for the number of feeder RFTs,the number of forward RF feeder links, the transmission frequencies forthe forward RF feeder links, the bandwidth of the forward RF feederlinks, and/or spectral efficiency. The forward RF feeder links couldalso utilize beam hopping, frequency reuse of 1, or other arrangementsrequiring more or less RF bandwidth.

In some implementations, such as in the example shown in FIG. 1, the RFfeeder links 130 also each include a respective reverse RF feeder linksignal (which may be referred to as a “reverse RF feeder link” or an “RFfeeder downlink”, and which encodes reverse-directed user data) receivedfrom the HAP 140. In this particular example, the same 40 feeder RFTstransmitting the forward RF feeder links are also receiving respectiveconcurrent reverse RF feeder links; each of the reverse RF feeder linksis received at a frequency of at least 60 GHz (in some examples, atleast 80 GHz) and has a bandwidth of 10 GHz (5 GHz with right-handcircular polarization (RHCP) and 5 GHz with left-hand circularpolarization (LHCP)), providing a total reverse RF feeder link bandwidthof 400 GHz from the HAP 140 to the feeder RFT array 128. With a MODCODproviding a spectral efficiency of 1.25 bps/Hz, a total reverse capacityof 500 Gbps is provided by the feeder RFT array 128. The HAP data center126 is configured to decode, demodulate, and demultiplex the reverse RFfeeder links and provide the resulting reverse data streams to thegateway 120. Also, the reverse RF feeder links could be part of aground-based beam forming system in which the reverse link wouldcomprise return link beam responses and possibly have a larger feederlink requirement.

The HAP 140 is adapted to be deployed in the stratosphere to carry apayload 144 (which may be referred to as a “high-altitude communicationdevice”). The payload 144 could be carried below the HAP 140 as shown,or alternatively it could be contained within the envelope 142 which, insome examples, could be an airship or aircraft. In some portions of thisdescription, the HAP 140 and the payload 144 may be referred tointerchangeably. At moderate latitudes, the stratosphere includesaltitudes between approximately 10 km and 50 km altitude above thesurface. At the poles, the stratosphere starts at an altitude ofapproximately 8 km. The HAP 140 may generally be configured to operateat altitudes between 17 km and 22 km while operating as an endpoint ofthe optical feeder link 150 (although other altitudes are possible).This altitude range may be advantageous for several reasons. Inparticular, this layer of the stratosphere generally has relatively lowwind speeds (for example, winds between 5 and 20 mph at lower latitudes)and relatively little turbulence. Further, while the winds between 17 kmand 22 km may vary with latitude and by season, the variations can bemodeled in a reasonably accurate manner. Additionally, altitudes above17 km are typically above the maximum flight level designated forcommercial air traffic. Therefore, interference with commercial flightsis not a concern when the HAP deployed between 17 km and 22 km altitude.

As noted above, the HAP 140 serves as an endpoint of the optical feederlink 150 between the HAP 140 and the satellite 160. Due to the altitudeat which the HAP 140 operates, this places the optical feeder link 150above much of the atmosphere, resulting in substantial reduction inatmospheric attenuations and distortions. At and above such altitudes,the atmosphere contains a minimal amount of dust, water, and otheratmospheric particles that often interfere with optical signals in thetroposphere. For example, 90% of the Earth's atmospheric mass lies belowan altitude of 16 km. Additionally, nearly all atmospheric water vaporor moisture, is found in the troposphere (the lowest layer of theatmosphere) which extends to an altitude of about 10-12 km. Thisincludes clouds, through which operating an optical link can beimpossible. Also, in the stratosphere, the next layer above thetroposphere, the air is very stable and turbulent mixing is inhibiteddue to an inverted temperature profile in the stratosphere.

In the example shown in FIG. 1, the HAP 140 is implemented using ahigh-altitude stratospheric balloon, including an envelope 142. Theenvelope 142 may take various forms, which may be currently well-knownor yet to be developed. For instance, the envelope 142 may be made ofmetalized Mylar or BoPet. Alternatively or additionally, some or all ofthe envelope 142 may be constructed from a highly-flexible latexmaterial or a rubber material such as chloroprene. Other materials arealso possible. Further, the shape and size of the envelope 142 may varydepending upon the particular implementation. Additionally, the envelope142 may be filled with various different types of gases, such as heliumand/or hydrogen. Other types of gases are possible as well. In someexamples, a thin-film photovoltaic may be provided on a portion of theenvelope 142 to provide power for the HAP 140, including the payload144. Although in FIG. 1 the HAP 140 is embodied as a high-altitudestratospheric balloon, other high-altitude platforms may be utilized,such as an airship.

As noted above, the HAP 140 serves as an endpoint of the RF feeder links130 between the HAP 140 and the feeder RFT array 128. For this purpose,the payload 144 includes a HAP-based RF feeder link antenna 146 (which,in some examples, may include multiple antennas) for receiving forwardRF feeder links from the feeder RFT array 128 and, in some examples,transmitting reverse RF feeder links to the feeder RFT array 128.

Ideally, the HAP 140 would operate directly above the feeder RFT array128, with a zenith distance of 0° with respect to the feeder RFT array128. However, the HAP 140 is expected to move about horizontally, suchas due to wind forces. Due to the compact arrangement and large numberof the feeder RFTs included in the feeder RFT array 128, the HAP 140must operate within a first lateral distance or angle of the feeder RFTarray 128 in order to achieve a target number of active RF feeder links130 corresponding to full bandwidth capacity without unacceptable levelsof interference among the RF feeder links 130 (in either the forward orreverse direction). The telecommunication system 100 may be configuredto perform station keeping operations for HAP 140 to maximize an amountof time that the HAP 140 operates within that particular lateraldistance or angle. In some examples, the station keeping operations mayaccount for the availability of multiple HAPs operating in proximity tothe feeder RFT array 128. Station keeping operations may include changesin the altitude of the HAP 140 to take advantage of winds of varyingspeeds and directions present at different altitudes.

The RF feeder link antenna 146 (which may also be referred to as a“gateway antenna”) may be implemented with a single multi-beam antennawith multiple feeds to provide the target number of active RF feederlinks 130 to reach full capacity. Changes in altitude may cause theangular spacing between the RF feeder links 130 to change. In someimplementations, the HAP 140 may be configured to change angular spacingof the RF feeder links 130 by mechanically moving feeds of the RF feederlink antenna 146. In some implementations, the RF feeder antenna link146 may be implemented using a phased array antenna (which may bereferred to as an “electronically steered antenna”), with whichelectronic beam steering can be performed. A phased array antennaprovides fast beam steering, including an ability to generatesimultaneous beams and dynamically adjust the characteristics of thebeam patterns. As a result, a phased array antenna offers improvedperformance over mechanical means for beam steering in response tomovements of the HAP 140.

In some implementations, 70-80 GHz or higher RF bands are suitable asthey allow multiple RF feeder terminals to be positioned in a compactarrangement in a relatively small area due to the small beam widths thatcan be achieved at these frequencies and extensive reuse that can beachieved in a small area, although other bands may be used as well.Additionally, use of very high RF frequencies, such as so-called“millimeter wave” frequencies, for the RF feeder links 130 permitsoperation from a single RF feeder link site 129, rather than anexpensive widely distributed backbone network with diverse sites. Maturetechnologies are available for such RF frequencies, such as technologiesdeveloped for terrestrial microwave and 5G cellular radio systems.Additionally, the compact size of the feeder RFT array 128 and the highdirectionality of the RF feeder links 130 reduces concerns about RFinterference with other RF applications.

As the RF feeder links 130 operate over a much smaller distance than aground-to-satellite RF link (such as the satellite RF link shown in FIG.1), adequate margin can be achieved to overcome E-band fading at asingle site, thus avoiding a need for diversity. Additionally, althougha site with generally clear weather conditions is favorable, a widerrange of locations are practical than with a ground to GEO RF linkoperating at a distance of approximately 36,000 km.

The following example RF link budget is illustrative for the RF feederlinks 130 with the HAP 140 operating at an altitude of 22 km (although alarger HAP antenna, which is more practical with a phased array antenna,yields narrower beams and a smaller feeder RFT array 128):

Free space loss at 22 km 156.2 dB Gas absorption loss (0.4 dB/km)  8.8dB Fade margin @ NLV 99.5%   25 dB RF feeder terminal antenna   60 cmdiameter Tx gain   50 dB RF feeder terminal EIRP   50 dBW (with 1 W PA)Rx noise figure   ~5 dB Ts   600K (27.8 dB) HAP antenna diameter   60 cmRx gain   50 dB G/T  22.2 dB/K C/No 110.8 dB (50 + 22.2 − 156.2 + 228.6− 25 − 8.8) Bandwidth    5 GHz (97 dBHz) C/N  13.8 dB

To accurately and precisely aim the plurality of beams of the HAP-basedRF feeder link antenna 146 to their respective RF feeder terminals inthe compactly arranged feeder RFT array 128, and maintain the RF feederlinks 130 while the HAP 140 moves around (with various, and sometimeshigh frequency, changes in roll, pitch, and yaw), the HAP 140 includesan antenna stabilizer mechanism. The antenna stabilizer mechanism mayinclude a mechanical antenna positioner (such as a 3-axis gimbal)configured to selectively orient, for example, a main reflector of theRF feeder link antenna 146, one or more mechanical antenna feedpositioners (which can more rapidly reposition individual feeds, whichhave significantly less mass than the main reflector), and/or a phasedarray antenna. For example, a mechanical antenna positioner can performcoarse/slow positioning and be used in combination with a phased arrayantenna respond to higher frequency changes in roll, pitch, and yaw ofthe HAP 140.

In some implementations, as in the example shown in FIG. 1, the payload144 may include one or more additional RF terminal communicationantennas 134 to provide one or more RF communication services forend-user RFTs 136, such as the illustrated ground-based RFT 136 a andthe air-based RFT 136 b. In some examples, a portion of the RF feederlinks 130 provides backhaul for these services. Due to the high altitudeat which the HAP 140 operates, a significant land area is within a fieldof view of the RF terminal communication antennas 134, facilitating useof spot beams and frequency reuse. Example RF communication servicesinclude, but are not limited to, cellular communication services andwireless internet access. Use of the HAP 140 for these other purposescan reduce or divide costs of operating the HAP 140. In some examples,one or more of the RF communication services is operated by a thirdparty different than the party operating the HAP 140 and/or thesatellite 160.

The payload 144 includes a HAP-based optical feeder communication system148 which is used to establish and maintain the optical feeder link 150in the form of one or more FSO links (for example, modulated laserlinks) between the HAP 140 and the satellite 160. The optical feederlink 150 may include an forward optical feeder link signal 152 (whichmay be referred to as a “forward optical feeder link” or an “opticalfeeder uplink”) transmitted by an optical transmitter included in theoptical feeder communication system 148 and received by the satellite160. The optical feeder link 150 may include an reverse optical feederlink signal 154 (which may be referred to as a “reverse optical feederlink” or an “optical feeder downlink”) transmitted by the satellite 150and received by an optical receiver included in the optical feedercommunication system 148. The payload 144 is configured to, via theoptical feeder communication system 148, convert and multiplex multipleforward link transmissions included in the RF feeder links 130 into theforward optical feeder link 152, and convert and demultiplex the reverseoptical feeder link 154 into multiple reverse RF feeder linktransmissions included in the RF feeder links 130. By operating theoptical feeder link 150 outside of the troposphere, many substantialoptical link issues encountered with FSO links through the troposphereare avoided, such as, but not limited to, cloud obstruction, the higherwater content of the troposphere, substantial turbulence in thetroposphere and resulting fading, and reduced wavelength-dependentrefraction (which could negatively impact the effectiveness of WDMoptical modulation schemes). By avoiding these issues, a need foroptical diversity (multiple optical links at geographically diverselocations) may be eliminated or reduced, the optical electronicssimplified, and an analog transparent architecture may possibly beenabled.

The optical feeder communication system 148 includes one or more opticaltelescopes including a combination of optics (such as refractive lensesand/or reflective mirrors) for transmitting and directing the forwardoptical feeder link 152 and/or the reverse optical feeder link 154. Insome examples, a single “duplex” optical telescope may be used for boththe forward optical feeder link 152 and the forward optical feeder link154. Use of a single optical telescope may simplify mechanical aspectsof pointing, acquisition, and tracking (PAT) of the optical feeder link150 between the HAP 140 and the satellite 160, as it reduces the problemto a single optical telescope that must perform PAT at approximatelymicroradian accuracy despite motion of the HAP 140 as it operates. Insome examples, the optical feeder communication system 148 includes afirst optical telescope for transmitting the forward optical feeder link152 and a second optical telescope for receiving the reverse opticalfeeder link 154. By having separate telescopes, the optical chains fortransmitting and receiving the optical feeder link 150 may be simplified(for example, by avoiding one or more beamsplitter and/or filterelements used in a duplex telescope), resulting in increased gain and/orsignal quality. Separate telescopes also help avoid or eliminate opticalcrosstalk between a sensor being used to capture a very weak reverseoptical feeder link 154 and transmission of a much stronger (forexample, by about 110 dB) forward optical feeder link 152. In someexamples, the optical feeder communication system 148 includes multipleoptical transmitters; for example, to reduce effects of turbulence or todivide the transmitted optical power among multiple telescopes, ratherthan demanding a single telescope suitable for a higher power opticalsignal.

The optical feeder communication system 148 is configured to accuratelyand precisely perform optical pointing for the optical feeder link 150while the HAP 140 rolls, pitches, yaws, climbs/descends, turns, andtranslates. Although, as discussed above, similar pointing operationsare performed for the RF feeder link antenna 146, a far higher degree ofprecision and accuracy is demanded for PAT of an optical signal with adivergence of approximately 15 microradians with a GEO satellite 160.Towards this purpose, the optical feeder communication system 148includes, for each optical telescope, a pointing mechanism thatsimultaneously performs motion stabilization and PAT.

For a 35,800 km space-based optical link, the following link budget foran optical link operating at 2.5 Gbps using 4-inch telescopes at boththe HAP 140 and the satellite 160 is illustrative:

Transmit power 40 dBm 10 W Frequency 193 THz Wavelength 1550 nm Txtelescope diameter 10.2 cm Tx telescope gain 109.3 dB Tx loss −2.0 dBStrehl ratio −0.4 dB Pointing loss −3.0 dB Beam divergence 19.3 μradBeam size at GEO 700 m Path loss −289.3 dB Rx telescope diameter 10.2 cmRx telescope gain 106.3 dB Rx loss −2.0 dB Receive power −41.1 dBmReceive sensitivity 90 photons/bit Required power −45.4 dBm Link margin4.3 dB

For 1 Tbps forward data capacity, using the same telescopes the transmitpower would be increased to an estimated 66 dBm, or approximately 4 kW.However, although in some implementations it is not desirable toincrease the size of the telescope aperture at the HAP 140 (for example,to reduce telescope mass for motion stabilization), the size of thetelescope aperture may be increased at the satellite 140, in view ofsubstantially reduced problem of motion stabilization, in order toachieve increase gain and achieve corresponding reductions in transmitpower. It is noted that the wavelength of 1550 nm is merely an example,and that other wavelengths may be used (including, but not limited to,other wavelengths around 1550 nm and wavelengths around 850 nm or 1064nm). In some implementations, wavelength division multiplexing (WDM) maybe used to concurrently operate the optical feeder link at multiplewavelengths, at lower individual bitrates, resulting in correspondingimprovements to the optical link budget. Dense wavelength divisionmultiplexing (DWDM) may be used to multiplex many optical channels intothe optical feeder link.

The space satellite 160 (which may simply be referred to as a“satellite”) serves as another endpoint of the optical feeder link 150,and as an endpoint for the RF service links 170. In the example shown inFIG. 1, the satellite 160 is a GEO satellite, with an orbit thatmaintains the satellite 160 over a fixed longitude of the Earth'ssurface. A GEO satellite 160, issues such as maintaining, distributing,and calculating ephemera of the orbit of the satellite 160 can beavoided, along with tracking satellite 160 across the sky, obstructionof a portion of the sky by the envelope 142, and optical link issueswhen the satellite 160 is at low elevations. However, in someimplementations, the satellite 160 can be a medium earth orbit (MEO) ora low earth orbit (LEO), and/or may be one of multiple satellitesoperating in a constellation of satellites. The satellite 160 isconfigured to convert and demultiplex the forward optical feeder link152 into transmissions for forward RF service links (for example, asforward RF service links 176 via respective spot beams 172) included inthe RF service links 170, and is configured to convert and multiplexmultiple reverse RF service link transmissions (for example, for reverseRF service links 118 and 178) included in the RF service links 170 intothe reverse optical feeder link 154. The satellite 160 includes asatellite-based optical feeder communication system 162, which may beconfigured much as described in connection with the HAP-based opticalfeeder communication system 148. However, as the satellite 160 does notexperience frequent changes in movement, tracking the HAP 140 issimplified, which may allow use of larger aperture telescopes despitethe accompanying increase in moving mass and narrower divergence. Insome implementations, the satellite 160 may concurrently operate as anendpoint for multiple different optical links 150 with multipledifferent HAPs 140 (which may be a different locations). For example,the satellite 160 might be configured to concurrently operate a firstoptical feeder link 150 with a first HAP 140 and a second optical feederlink 150 with a second HAP 140. To avoid optical crosstalk, the multipleforward optical feeder links 152 may be operated in different bands,such as a first forward optical feeder link in the ITU C-band (1530-1565nm) and a second forward optical feeder link in the ITU L-band(1565-1625 nm). The ITU S-band (1460-1530 nm), the U-band (1625-1675nm), and/or the 3-5 μm portion of the CIE IR-C band may also be used forthe optical feeder link 150, although there are fewer commercial productoptions in these bands due to the dominance of the ITU C-band forlong-distance telecommunications. For example, DWDM hardware is mostlyavailable for the ITU C-band and the ITU L-band.

The satellite 160 includes a satellite-based RF communication system 164which is used for the RF service links 170, including transmittingforward RF service links 176 (such as the forward RF service link 176 b)to end user service RFTs 112 and receiving reverse RF service links 178(such as the reverse RF service links 178 ba, 178 bb, and 178 cd) fromthe end user service RFTs 112. An end user service RFT 112 may also bereferred to as a “user terminal” (UT) or more simply an “RFT”. In someexamples, the RF service links 170 are in one or more fixed satelliteservice downlink frequency bands, such as, but not limited to, theQ-band at 40-42 GHz, the Ka-band in the 18-20 GHz range, and the Ku-bandin the 12-18 GHz range. Use of RF service links 170 in these moretraditional bands facilitates user of lower cost end user service RFTs112 and/or use of existing end user service RFTs 112. An end userservice RFT 112 may be connected to one or more items of user equipment(UE) 114 (such as the UE 114 bb) which may be associated with one ormore end users 110.

In some implementations, as shown in FIG. 1, the RF communication system164 provides the RF service links 170 via multiple spot beams 172covering respective regions 174 (such as the spot beams 172 a, 172 b,and 172 c for respective regions 174 a, 174 b, and 174 c). For each spotbeam 172 there is a single respective forward RF service link 176 (suchas the forward RF service link 176 b for the spot beam 172 b), andmultiple reverse RF service links 178 (such as the reverse RF servicelinks 178 ba, 178 bb, and 178 cd for respective RFTs 112 ba, 112 bb, and112 cd) via a variety of multiplexing techniques. In some examples, asingle forward RF service link 176 may utilize multiple carriers or usea multicarrier modulation such as orthogonal multicarrier modulation(OFDM). The use of spot beams 172 may be combined with frequency reuse,in which the spot beams 172 are operated in multiple “colors” withdifferent combinations of frequency ranges and polarization. With theuse of spot beams 172, the RF communication system 164 can achievehigher gain and greater total capacity. Additionally, thetelecommunication system 100 may be configured to selectively anddynamically reallocate bandwidth to the spot beams 172.

In some implementations, the HAP data center 126 includes a satelliteRFT 166 used to operate a satellite RF link 168 between the HAP datacenter 126 and the satellite 160 for use as a command/control channelwith the satellite 160. Another RF link (not shown in FIG. 1) may beestablished between the HAP data center 126 and the HAP 140 as acommand/control channel with the HAP 140. The HAP data center 126 may beconfigured to use these RF links for command/control operations forsatellite 160 and/or HAP 140. Such operations may include, but are notlimited to, obtaining location and/or movement information from the HAP140, control station keeping operations performed by the HAP 140,coordinate station keeping operations among multiple HAPs 140,facilitating PAT of the optical feeder link 150 (for example, byreducing acquisition time), and/or facilitating PAT of optical linksbetween HAPs 140. In some implementations, an RF link may be establisheddirectly between the HAP 140 and the satellite 160, and the HAP 140 andthe satellite 160 are configured to utilize the RF link to exchange datafacilitating PAT of the optical feeder link 150.

FIG. 2A illustrates a plan view of an example of the feeder RFT array128 shown in FIG. 1. In this example, the feeder RFT array 128 has 40feeder RFTs 210, including the labeled feeder RFTs 210 a, 210 b, 210 c,210 d, 210 e, 210 f, 210 g, 210 h, and 210 n. The feeder RFT array 128may include more or less than the illustrated 40 feeder RFTs 210 torealize various implementation goals, such as, but not limited to, atarget total operating capacity of the RF feeder links 130, a maximumtotal operating capacity of the RF feeder links 130, and/or an amount of“spare” feeder RFTs 210 to avoid reductions in operating capacityarising maintenance or failures of the feeder RFTs 210. As notedpreviously, the feeder RFTs 210 of the feeder RFT array 128 arecollocated together at a single RF feeder site 219 (which may bereferred to as a “location” of the feeder RFT array 128 and its feederRFTs 210), which offers substantial reductions in network costs overother feeder architectures involving multiple feeder sites at differentlocations.

In some implementations, the feeder RFTs 210 are individually steerablevia respective beam steering mechanisms. A beam steering mechanismincluded in a feeder RFT 210 may include a mechanical antenna positioner(such as a 2-axis gimbal) configured to selectively orient, for example,a main reflector of the feeder RFT 210, a mechanical antenna feedpositioner (which can more rapidly reposition a feed, which hassignificantly less mass than the main reflector), and/or a phased arrayantenna. For example, a mechanical antenna positioner can performcoarse/slow positioning and be used in combination with a phased arrayantenna respond to higher frequency changes in azimuth and elevation ofthe HAP 140.

In FIG. 2A, each of the feeder RFTs 210 is shown within a respective RFTcell 212, including feeder RFTs 210 a, 210 b, 210 c, 210 d, 210 e, 210f, 210 g, 210 h, and 210 n within respective RFT cells 212 a, 212 b, 212c, 212 d, 212 e, 212 f, 212 g, 212 h, and 212 n). The RFT cells 212 arenot physical elements of the feeder RFT array 128, but insteadillustrate that the feeder RFTs 210 are positioned in a compactarrangement with distances between adjacent feeder RFTs 210 thatmaintains interference among the RF feeder links 210 below an acceptableor target level. In the example shown in FIG. 2A, each of the cells 212is circular and has the same RFT cell diameter 220 (as shown for the RFTcell 212 h). As a result, each feeder RFT 210 is at least the distanceof the RFT cell diameter 220 from any other feeder RFT 212. The RFT celldiameter 220 may also be referred to as a minimum distance betweenindividual feeder RFTs 210. It is noted that other shapes and/or sizescan be used for the RFT cells 212, and that shapes, sizes, and ororientations can be different among the RFT cells 212. For example, theRFT cells 212 might vary in size in accordance with a distance from acenter of the feeder RFT array 128, with larger RFT cells 212 around theperiphery, to reduce interference at increased zenith distances for theHAP 140 at which the feeder RFT array 128 is viewed obliquely from theHAP 140. Sizes of the RFT cells 212 may account for frequency reusefactor for the RF feeder links 130, which permits for smaller RFT cellsizes. Use of a larger HAP-based RF feeder link antenna 146 allowsnarrower beams to be formed for the RF feeder link 130, which allows forsmaller RFT cell sizes to be used. Additionally, an expected maximumoperating altitude for the HAP 140 will affect the RFT cell sizes.

In FIG. 2A, the RFT cells 212 are positioned in a compact circulararrangement, with all of the RFT cells 212 fitting within, and beingencompassed by, a circular area 230 with a diameter 232 (which may alsobe referred to as a “span” of the feeder RFT array 128). An arrangementof the RFT cells 212 that minimizes the diameter 232 is considered themost “compact” arrangement of the RFT cells 212 and the feeder RFTs 210positioned therein. In FIG. 2A, the feeder RFTs 210 connect with the HAPdata center 126 by a local network of wire and/or fiber data links (seecommunication link 260). By reducing the diameter 232, a correspondingland area for installing and operating the RF feeder array 130 isreduced, as well as the lengths of power and signal couplings for the RFfeeder array 130. Also, the more compact the arrangement of RFTs 210,the less stringent the design requirements will be on the HAP-based RFfeeder link antenna 146. Compact arrangements of the feeder RFT array128 minimize the lengths and costs of the local network, in contrast toconventional use of wide area fiber network connections betweendifferent cities where RFTs are located. In this example, the 40 RFTcells 212 are arranged to occupy approximately 79% of the circular area230. FIG. 2A also illustrates a square area 240 with sides havinglengths equal to the diameter 232, which illustrates an example of atract of land that might be used to construct the RF feeder array 128.Additionally, FIG. 2A illustrates a second circular area 250, with adiameter 252, which represents a smallest circular area encompassing thecenter points of the feeder RFTs 210, which closely corresponds an areain which the feeder RFTs 210 may all be constructed.

FIG. 2B illustrates an alternative compact arrangement of the 40 feederRFTs 210 shown in FIG. 2A, with the RFT cells 212 arranged hexagonally.However, with this arrangement, the 40 RFT cells 212 occupy onlyapproximately 64% of the circular area 230, and the diameter 232 isincreased by about 11% over the more compact arrangement shown in FIG.2B. For purpose of further illustration, FIG. 2C illustrates an exampleof the feeder RFT array 128 with 61 feeder RFTs 210, and FIG. 2Dillustrates an example of the feeder RFT array 128 with 79 feeder RFTs210. In addition to providing greater numbers of feeder RFTs 210, theexamples shown in FIGS. 2C and 2D also have rotational symmetry, whichcan facilitate accommodating rotation of the HAP 140 in establishingand/or maintaining the RF feeder links 130.

Tables 1-5 below provide illustrative examples of RFT cell sizingconsiderations and dimensions for the RFT feeder terminal array 128,with collocation of the feeder RFTs 210 at a single location, accordingto various design parameters for the feeder RFT arrangements shown inFIG. 2A (with 40 feeder RFTs), FIG. 2C (with 61 feeder RFTs), and FIG.2D (with 79 feeder RFTs). For these examples, it may be assumed each RFTterminal 210 would offer 10 GHz forward bandwidth (81-86 GHz with twopolarizations in the forward direction, although frequencies of 71-76GHz in the reverse direction, also with two polarizations, areconservatively represented as 70 GHz below to illustrate a maximumspacing) and 2.5 bits/Hz (thus requiring a total of 400 GHz forward RFbandwidth for 1 Tbps forward data capacity). This would involve at least40 feeder RFTs (as shown in FIG. 2A) to support 1 Tbps forward datacapacity. Table 1, below, shows, for two HAP antenna sizes of 60 cm and200 cm, RFT cell sizing considerations involving a frequency reusefactor of 1 and altitudes of 15 km and 22 km for the HAP 140. The RFTreuse spacing is computed for a reuse factor of 1 and for a hexagonalgrid with spacing R·√{square root over (3)}, where R is half of the halfpower beam width (HPBW). Additional margin is added to the calculatedspacing to be conservative.

TABLE 1 RF Feeder Antenna Array Cell Sizing Considerations HAP AntennaSize 200 cm 60 cm Frequency (Reverse Links) 70 GHz 70 GHz HPBW (21/(fD))@ 70 GHz 0.15° 0.50° HPBW (21/(fD)) @ 80 GHz 0.13125° 0.4375° ReuseSpacing (R · {square root over (3)}) 0.130° 0.433° Reuse Spacing (15 km)34 m 114 m Reuse Spacing (22 km)/ 50 m 167 m RFT cell diameter (use 75m) (use 200 m)

Tables 2 and 3, below, show the resulting dimensions for the feeder RFTarray 128 with 40 cells, 61 cells, 79 cells, and 109 cells where theHAP-based RF feeder link antenna 146 has a diameter of 200 cm.

TABLE 2 Example RF Feeder Array Dimensions for 200 cm Antenna (75 m cellsize) (encompassing cells, as shown for circular area 230) Number ofcells 40 61 79 109 Array Diameter (m) 535 650 743 868 Circular Area(acres) 56 82 108 146 Square Area (acres) 71 105 137 186 Angular FOV @15 km 2.04° 2.48° 2.84° 3.32° Angular FOV @ 22 km 1.40° 1.70° 1.94°2.26°

TABLE 3 Example RF Feeder Array Dimensions for 200 cm Antenna (75 m cellsize) (encompassing only centers of feeder RFTs, as shown for circulararea 250) Number of cells 40 61 79 109 Array Diameter (m) 464 579 672797 Circular Area (acres) 42 65 88 123 Square Area (acres) 53 83 112 157Angular FOV @ 15 km 1.77° 2.21° 2.57° 3.04° Angular FOV @ 22 km 1.21°1.51° 1.75° 2.08°Thus, according to the conditions used for Tables 2 and 3, the feederRFT array 128, usable for a forward data capacity of at least 1 Tbps,can be constructed with the margins offered by 79 feeder RFTs (roughlydouble those offered by 40 feeder RFTs) within diameters 230 and 250 ofless than 800 meters, a total operating beam width for the RF feederlinks 130 of less than 2.9°, and an FOV of less than 2.6°. With themargins offered by 61 RFTs (roughly 50% more than offered by 40 feederRFTs), the feeder RFT array 128 can be constructed within diameters 230and 250 of less than 700 meters, a total operating beam width for the RFfeeder links 130 of less than 2.5°, and an FOV of less than 2.3°.

Tables 4 and 5, below, show the resulting dimensions for the feeder RFTarray 128 with the same 40 cells, 61 cells, 79 cells, and 109 cells, butwhere the HAP-based RF feeder link antenna 146 has a reduced diameter of60 cm, resulting in increased beam widths for the RF feeder links 130.

TABLE 4 Example RF Feeder Array Dimensions for 60 cm Antenna (200 m cellsize) (encompassing cells, as shown for circular area 230) Number ofcells 40 61 79 109 Array Diameter (m) 1425 1732 1981 2313 Circular Area(acres) 394 583 762 1038 Square Area (acres) 502 742 970 1322 AngularFOV @ 15 km 5.44° 6.61° 7.56° 8.82° Angular FOV @ 22 km 3.71° 4.51°5.16° 6.02°

TABLE 5 Example RF Feeder Array Dimensions for 60 cm Antenna (200 m cellsize) (encompassing only centers of feeder RFTs, as shown for circulararea 250) Number of cells 40 61 79 109 Array Diameter (m) 1229 1536 17852117 Circular Area (acres) 293 458 619 870 Square Area (acres) 374 583788 1107 Angular FOV @ 15 km 4.70° 5.87° 6.82° 8.08° Angular FOV @ 22 km3.20° 4.00° 4.65° 5.51°Thus, according to the conditions used for Tables 4 and 5, the feederRFT array 128, usable for a forward data capacity of at least 1 Tbps,can be constructed with the margins offered by 79 feeder RFTs (roughlydouble those offered by 40 feeder RFTs) within a diameter 230 of 2000meters and a diameter 250 of less than 1800 meters, a total operatingbeam width for the RF feeder links 130 of less than 7.6°, and an FOV ofless than 6.9°. With the margins offered by 61 RFTs (roughly 50% morethan offered by 40 feeder RFTs), the feeder RFT array 128 can beconstructed within a diameter 230 of 1800 meters and a diameter 250 ofless than 1600 meters, a total operating beam width for the RF feederlinks 130 of less than 6.7°, and an FOV of less than 6°. As can be seenfrom Tables 2-5, the decrease from 200 cm to 60 cm results inapproximately a 7-fold increase in the area for the feeder RFT array128. Despite this, the providing the RF feeder links 130 with a singlelocation can still be significantly more cost effective thanarchitectures involving diversity sites.

As shown in FIGS. 1 and 2, the HAP data center 126 is communicativelycoupled to the feeder RFT array 128 via a communication link 260 and isconfigured to control operation of the feeder RFTs 210, generate forwardRF feeder link signals for transmission to the HAP 140 via the RF feederlinks 130, provide the generated forward RF feeder link signals to thefeeder RFTs for transmission, obtain reverse RF feeder link signalsreceived by the feeder RFTs from the HAP 140 via the feeder links 130,and process the obtained reverse RF feeder link signals. For example,HAP data center 126 may be configured to provide signals to, and receivesignals from, the feeder RFTs 210 via electronic cables and/or opticalfiber included in the communication link 260.

FIG. 3 illustrates further details of the payload 144 of the HAP 140shown in FIG. 1 and examples of operations performed by the payload 144in connection with the RF feeder links 130 and the optical feeder link150. At the time illustrated in FIG. 3, the HAP 140 is positioned at analtitude 330 directly above the feeder RFT array 128 with a zenithdistance of 0°. At the bottom of FIG. 3 is shown a portion of the feederRFT array 128 with 40 feeder RFTs 210 shown in FIG. 2A. Morespecifically, FIG. 3 shows the feeder RFTs 210 a, 210 b, 210 c, 210 d,210 e, 210 f, and 210 g, within their respective RFT cells 212 a, 212 b,212 c, 212 d, 212 e, 212 f, and 212 g. A plurality of RF feeder links130 are concurrently operating between the feeder RFT array 128 and theHAP 140, including RF feeder links 310 a, 310 b, 310 c, 310 d, 310 e,310 f, and 310 g, corresponding to respective feeder RFTs 210 a, 210 b,210 c, 210 d, 210 e, 210 f, and 210 g, including their respectivereverse RF feeder links 312 a, 312 b, 312 c, 312 d, 312 e, 312 f, and312 g (transmitted by respective feeds of the RF feeder link antenna 146and having expanded to the shaded areas in the bottom portion of FIG. 3)and their respective forward RF feeder links 314 a, 314 b, 314 c, 314 d,314 e, 314 f, and 314 g (transmitted by the feeder RFT array 128 andreceived by respective feeds of the RF feeder link antenna 146).

FIG. 3 shows various angles with respect to the RF feeder link antenna146 (which may also be referred to as FOV angles). The illustratedangles are dependent on the altitude 330 and, for some of theillustrated angles, by the zenith direction of the HAP 140 relative tothe feeder RFT array 128. For purposes of the description of theseangles in FIG. 3, RF feeder link antenna 146 has a diameter of 200 cm,the HAP is at an altitude 330 of 22 km, all of the reverse RF feederlinks are at a frequency of 70 GHz, and the corresponding portions ofTables 1-3 apply. Angle θ₃₂₀ is an angular beam width of the reverse RFfeeder link 312 f, such as a half power beam width (HPBW); in thisexample, angle θ₃₂₀ is approximately 0.15°. In this example, all of thereverse RF feeder links have approximately the same angular beam width.Angle θ₃₂₂ is an angular separation of adjacent feeder RFTs 310 b and310 c. Angle θ₃₂₃ is an angular width of the RFT cell 212 d. In thisexample, all of the RFT cells 212 have approximately the same diameterof 75 meters and angles θ₃₂₂ and θ₃₂₃ are both approximately 0.196°.Angle θ324 is the angular width of the circular area 250 (with diameter232 at ground level); approximately 1.21° in this example. Angle θ₃₂₆ isthe angular width of the smallest circle encompassing the beam widths ofthe reverse RF feeder links; approximately 1.36° in this example. Angleθ₃₂₈ is the angular width of the circular area 230 (with diameter 252 atground level); approximately 1.40° in this example.

The payload 144 includes a power supply 342 to supply power to thevarious components of the payload 144. The power supply 342 may includea rechargeable battery. In other embodiments, the power supply 342 mayadditionally or alternatively include other means known in the art forproducing power. In addition, the HAP 140 may include a solar powergeneration system, such as a thin film photovoltaic surface included inthe envelope 142. The solar power generation system may include solarpanels and could be used to generate power that charges and/or isdistributed by the power supply 342.

The payload 144 includes one or more processors 350 and on-board datastorage (not shown in FIG. 3) including instructions which, whenexecuted by the processors 350, cause the payload 144 to perform theoperations described herein. The payload 144 also includes varioussensors 340 that may be used to determine changes in position andorientation of the payload 144 and capture environmental data, and thepayload 144 is configured to determine changes in position andorientation of the payload 144 (including, for example, changes inposition and orientation of the RF feeder link antenna 146 and/or thetelescope 382) based on at least sensor data obtained from the sensors340. The sensors 340 may include, for example, one or more video and/orstill cameras, a satellite positioning system (for example, GPS orGLONASS), various motion sensors (for example, accelerometers,gyroscopes, and/or compasses), a star field tracker for orientationestimation based on celestial objects, and environmental sensorsoperable to measure environmental data such as, but not limited to,pressure, altitude, temperature, relative humidity, and/or wind speedand/or direction.

The payload 144 includes an RF feeder communication system 360 that isconfigured to transmit and receive RF signals for the RF feeder links130. The RF feeder communication system 360 includes a forward RF feederlink receiver 364 (labeled “RF RX” in FIG. 3) configured to receivemultiple forward RF feeder links from the feeder RFT array 128. The RFfeeder communication system 360 also includes a reverse RF feeder linktransmitter 362 (labeled “RF TX” in FIG. 3) configured to concurrentlytransmit multiple reverse RF feeder links to respective feeder RFTs ofthe feeder RFT array 128. The RF feeder communication system 360includes a beam orientation controller 366, which is configured tomaintain the beams of the HAP-based RF feeder link antenna 146 inorientations toward their respective feeder RFTs 210 while the payload144 moves around, such as by issuing commands to mechanical actuatorsand/or a phase array antenna.

The payload 144 also includes the optical feeder communication system148 that is configured to transmit the forward optical feeder link 152to the satellite 160 and receive the reverse optical feeder link 154from the satellite 160. The optical feeder communication system 148includes a steerable telescope 382 with an aperture 384. The opticalfeeder communication system 148 includes an forward optical feeder linktransmitter 370 (labeled “OPTICAL TX” in FIG. 3) configured to generatethe forward optical feeder link 152 from signals received via the RFfeeder links 130. The optical feeder communication system 148 alsoincludes an reverse optical feeder link receiver 372 (labeled “OPTICALRX” in FIG. 3) configured to receive the reverse optical feeder link 154and convert it into a signal suitable for generating portions of the RFfeeder links 130.

The optical feeder communication system 148 also includes a PATcontroller 380, which is configured to accurately and precisely performoptical pointing for the optical feeder link 150 between the payload 144and the satellite 160 using commands to a pointing mechanism 336 for thetelescope 382 while the payload 144 moves around. For example, thecommands may be generated based on at least information received fromthe sensors 340 and/or optical sensing devices included in the opticalfeeder communication system 148 (such as, but not limited to, an opticalquadrant detector and/or pixel-based optical detector receiving aportion of the reverse optical feeder link 154 via a beamsplitter). Thepointing mechanism 336 may include multiple different actuators such as,but not limited to, a 2-D or 3-D gimbal for slow and coarse pointing ofthe telescope 382, and one or more steered optical elements (such as,but not limited to, two-axis steering of a low mass secondary opticalelement, such as a secondary reflector) that perform rapid and finepointing of the optical feeder link 150. In some examples, the PATcontroller 380 attempts to ensure that the satellite 160 (or an opticalsignal emitted by the satellite) remains in an FOV of the telescope 384,and rapidly adjusts a pointing angle of a low-mass secondary opticalelement to more precisely target the optical feeder link 150. In someimplementations, the optical feeder communication system 148 may beconfigured to do wavefront correction of the optical feeder link 150 tocounter atmospheric turbulence encountered by the optical feeder link150. In some implementations, optical beam pointing may be performed inwhole or in part by means of phased-array optics.

The HAP 140 may be configured for altitude control. For instance, theHAP 140 may include a variable buoyancy system, which is configured tochange the altitude 330 of the HAP 140 by adjusting the volume and/ordensity of the gas in the envelope 142. A variable buoyancy system maytake various forms and may generally be any system that can change thevolume and/or density of gas in envelope 142. In some examples, the HAP140 may include a propulsion system used to perform station keeping.

The telecommunication system 100 may include a navigation system for theHAP 140. The navigation system may implement station-keeping functionsto maintain position within and/or move to a target position. In someexamples, the navigation system may use altitudinal wind data todetermine altitudinal adjustments that result in the wind carrying theHAP 140 in a desired direction and/or to a desired location. Thealtitude-control system may then make adjustments to the density of theenvelope 140 in order to effectuate the determined altitudinaladjustments and cause the HAP 140 to move horizontally to the desireddirection and/or to the desired location. The altitudinal adjustmentsmay be computed by the HAP data center 126 and communicated to the HAP140.

In some implementations, motion stabilization performed by the beamorienting controller 366 and/or the PAT controller 380 may beimplemented using a Kalman filter utilizing sensor data, such as fromthe sensors 340, and a last-known motion vector for the payload 144 asinputs to the Kalman filter that could output a predicted relativelocation, pose, and control signals for stabilization to adjust thepointing axis based on the predicted relative location and/or pose. TheKalman filter could be performed many times per second. For instance,PAT controller 380 could control the pointing mechanism 336 for thetelescope 382 to move from an initial axis towards a predicted targetaxis in an effort to compensate for motion of the payload 144 and tomaintain the optical feeder link 150 with the satellite 160. The Kalmanfilter method could use as inputs various sensor data (e.g., GPS data,inertial navigation data, camera images, etc.) so as to generatepredicted values. The system state predictions from the Kalman filtermethod may typically be more accurate than, for instance, utilizing datafrom only one sensor, as data from many types of sensors include noise,jitter, and generally imperfect sensor data.

The Kalman filter cycle could involve two main phases: a predictionphase and an update phase. In the prediction phase, the payload 144could predict the current pose using a physical model of the payload144, the HAP 140, and its environment plus any perturbations to othersystem variables, for instance, wind velocity, heading, andacceleration. Additionally, a covariance (a measure of how much tworandom variables, such as wind velocity and HAP 140 pose or payload 144pose, change together) related to the predicted pose could becalculated. In the update phase, the payload 144 could receive GPS dataor data relating to one or more RF feeder links 130 and/or the opticalfeeder link 150 indicating a degree to which they are accuratelypositioned. The positioning data could be used to update the initialpredicted pose to obtain an updated pose. The predicted and updatedposes could be used as inputs and weighted based on their associatedcovariances. The output of the Kalman filter method could provide apredicted pose that could be thus used to adjust the pointing angle ofthe RF feeder link antenna 146 or telescope 382 so as to maintain the RFfeeder links 130 or the optical feeder link 150.

In some implementations, diversity may be provided by having multipleHAPs 140 and/or having multiple RF feeder terminal arrays 128 atmultiple different sites. An optical fiber distribution network could beused to connect multiple diverse sites, each capable of serving theentire feeder link needs, and preferably offering sites with weatherconditions that are generally uncorrelated with weather conditions atother sites. In general, only one station would be active at a time.Both the satellite and the ground network would be configured tocoordinate the diversity switching operations. Determining the numberand locations of the diverse sites would be a system engineeringactivity using cloud statistics from various weather satellites such asMODIS, AQUA, and TERRA. Research on climate change and weatherforecasting has created a massive cloud database called the GlobalEnergy and Water cycle Experiment (GEWEX) Cloud Assessment Database;such a database may be utilized for these determinations.

FIG. 4 illustrates further details of the satellite 160 shown in FIG. 1and examples of operations performed by the satellite 160 in connectionwith the optical feeder link 150 with the HAP 140 and the RF servicelinks 170 with end user RFTs 112. In some examples, the satellite 160 isconfigured to transmit a beacon beam 410, with a higher divergence thanthe reverse optical feeder link 154 (for example, from about 1milliradian to about 50 milliradians), which can be used by the opticalfeeder communication system 148 to more quickly acquire the opticalfeeder link 150 with the satellite 160. In some examples, the HAP 140 isalso configured to transmit a beacon beam toward the satellite 160 toassist the optical feeder communication system 162 in more quicklyacquiring the optical feeder link 150 with the HAP 140. Thesatellite-based optical feeder communication system 162 operates much asdescribed for the HAP-based optical feeder communication 148, includingperforming steering of an optical telescope 420 with an aperture 422. Asnoted previously, as the satellite 160 does not undergo the degree andfrequency of motion changes experienced by the platform 144, it ispractical for telescope 420 to have a larger aperture 422 to increasegain for the optical feeder link 150. As the diameter of the reverseoptical feeder link 154 is smaller than the range that the HAP 140 mayoperate, steering of the reverse optical feeder link 154 is required.

Although, as in FIG. 1, only three spot beams 172 a, 172 b, 172 c areshown for the satellite 160, in many implementations there is a largernumber of spot beams 172; for example, there may be hundreds or over onethousand spot beams 172.

FIG. 5 illustrates an example of generating from network data a forwardRF feeder link included in a high capacity set of forward RF feederlinks, as may be performed under control of, and performed at least inpart by, the HAP data center 126 shown in FIGS. 1 and 2A. In thisexample, generation of one of the 40 forward RF feeder links, theforward RF feeder link 314 a, is shown. This is performed in paralleland in real-time for each of the forward RF feeder links in the RFfeeder links 130, resulting in a total of 1 Tbps of forward datacapacity from the HAP data center 126 to the payload 144 of the HAP 140.

The HAP data center 126 receives from the gateway 120 a respectiveforward feeder link data stream for each of the spot beams 172. FIG. 5shows the HAP data center 126 receiving 20 spot beam forward feeder linkdata streams. The HAP data center 126 is configured to multiplexupstream signals for multiple spot beams 172 into forward feeder linkbeam (which may also be referred to as a “forward feeder channel” or an“uplink feeder channel”). In the examples shown in FIGS. 5-7, a forwardfeeder link beam will not be demultiplexed into its constituent spotbeams until it is received by the satellite 160. As shown in FIG. 5, twoforward RF feeder link beams are generated for and concurrentlytransmitted by each active feeder RFT 210 in a respective forward RFfeeder link 314. A first forward RF feeder link beam 560 a (in FIG. 5,“Beam 1”) is transmitted by a feeder RFT 210 (in FIG. 5, feeder RFT 210a) with right hand circular polarization (RHCP), and a second forward RFfeeder link beam 560 b (in FIG. 5, “Beam 2”) is transmitted by the samefeeder RFT 210 with left hand circular polarization (LHCP). The HAP datacenter 126 includes and operates a respective forward RF feeder linkbeam generator 510 for each of the forward RF feeder link beams 560. InFIG. 5, a first forward RF feeder link beam generator 510 a receives 10spot beam forward feeder link data streams 502 a (labeled “Beam 1, Spot1” through “Beam 1, Spot 10”) and generates the corresponding firstforward RF feeder link beam 560 a for forward RF feeder link 314 a, anda second forward RF feeder link beam generator 510 b receives anadditional 10 spot beam forward feeder link data streams 502 b (labeled“Beam 2, Spot 1” through “Beam 2, Spot 10”) and generates acorresponding second forward RF feeder link beam 560 b for dualpolarization forward RF feeder link 314 a. In some examples, the RHCPand LHCP RF signals included in the forward RF feeder link 314 a may beconsidered two separate forward RF feeder links transmitted by the samefeeder RFT 210 a.

The first forward RF feeder link beam generator 510 a includes anencoder 520, a modulator 522, and an up-converter (“UpCo”) 530 for eachof the spot beam forward feeder link data streams 502 a (for example, inFIG. 5, the first forward RF feeder link beam generator 510 a includes10 encoders 520 aa through 520 aj, 10 respective modulators 522 aathrough 522 aj, and respective 10 up-converters 530 aa through 530 ajfor the 10 respective spot beam forward feeder link data streams 502 a).Each encoder 520 is configured to encode a respective spot beam forwardfeeder link data stream according to a selected forward error correction(FEC) technique, and a supported FEC may be performed according to oneor more provided parameters (for example, an FEC rate). Each modulator522 is configured to modulate its spot beam forward feeder link datastream according to a selected MODCOD scheme, and a supported MODCOD maybe performed according to one or more provided parameters. The HAP datacenter 126 is configured to specify a FEC technique, a MODCOD scheme,and associated parameters, and the HAP data center 126 may choose theFEC technique, the MODCOD scheme, and/or parameters according toinstructions received from the gateway 120. Different FEC techniques,MODCOD schemes, and/or parameters may be applied to spot beam forwardfeeder link data streams in the same forward feeder link beam. In someimplementations, the HAP data center 126 may use DVB-S2X Adaptive Codingand Modulation to select which FEC and MODCOD is used. In this example,the FEC encoding results in 1.25 Gbps data streams, and the appliedmodulation has a spectral efficiency of 2.5 bits/Hz, resulting in a 500MHz baseband signal for each of the spot beam forward feeder link datastreams. With 800 spot beam forward feeder link data streams multiplexedinto 80 forward feeder link beams, the 40 forward RF feeder linksdeliver 1 Tbps of total forward data capacity to the HAP 140.

FIG. 6 illustrates an example of generating, at the HAP 140, the forwardoptical feeder link 152 from the high capacity set of RF feeder links130 received from the feeder RFT array 128, including, for example, theforward RF feeder link 314 a shown in FIG. 5. In this example, 80forward RF feeder link beams are received via 40 forward RF feederlinks, each forward RF feeder link beam is downconverted to a lower RFband (for example, with a downconverter, or “DoCo,” such asdownconverters 640 aa and 640 ab), and the downconverted RF signal ismodulated onto a laser beam with an optical wavelength assigned to theforward feeder link beam (for example, Beam 1 is modulated onto anoptical beam with wavelength λ₁, Beam 2 at wavelength λ₂, and so on)using an electrical to optical (EO) converter (for example, by applyingradio over fiber, or “RoF,” techniques, such as with EO converters 650aa and 650 bb). In some examples, a Mach Zehnder Modulator is used forthe electrical to optical modulation. In some implementations, as shownin FIG. 6, each beam is assigned to a respective WDM channel (forexample, a DWDM channel) with a respective wavelength. In someimplementations, multiple beams may be downconverted to differentfrequencies and together be assigned to a WDM channel; for example,Beams 1 and 2 could be modulated onto an optical beam with a firstwavelength, Beams 3 and 4 modulated onto an optical beam with adifferent second wavelength, and so on. ITU-T G.694.1 defines a DWDMspectral grid for the ITU C-, L-, and S-bands with channel spacingsranging from 12.5 GHz to 100 GHz. For example, with 50 GHz channelspacing, the ITU C-band and the ITU L-band can each be used to provide100 channels. Use of different wavelength bands may permit a duplexoptical transceiver that transmits in one of the C-, S-, or L-band andreceives in a different one of the C-, S-, or L-band. A WDM multiplexer660 combines the 80 optical signals into a single multiplexed opticalsignal 662, which is provided to an optical amplifier 670, such as adoped fiber amplifier (for example, a Erbium, Ytterbium, orThulium-doped fiber amplifier), tapered amplifier, semiconductor opticalamplifier, Raman amplifier, and/or a parametric amplifier to produce theforward optical feeder link 152 for transmission to the satellite 160.In some implementations, optical amplification may be performed beforeWDM multiplexing. The multiplexed forward optical feeder link 152 uses80 WDM channels, each used to carry 5 GHz of capacity, for a total of400 GHz of bandwidth providing 1 Tbps forward data capacity.

FIG. 7 illustrates an example of the satellite 160 shown in FIGS. 1 and4 converting the forward optical feeder link 152 received from the HAP140 into corresponding RF service links 170 for multiple spot beams 172.First, the received WDM forward optical feeder link 152 is amplified byan optical amplifier 710 to an optical power level of at least 100 mW.The resulting amplified WDM forward optical feeder link 152 is providedto a WDM demultiplexer 720, which is configured to demultiplex theamplified forward optical feeder link 152 into its constituent WDMchannels (which may be referred to as “optical channel signals”) withrespective wavelengths λ₁, λ₂, . . . λ₈₀. As shown in more detail forthe wavelength λ₁, the WDM channels for each of the wavelengths λ₁-λ₈₀are converted into demultiplexed RF spot beam signals similar to thoseoutput by the modulators 522 in FIG. 5. The demultiplexed RF spot beamsignals are “colored” for frequency reuse by upconverting them toappropriate frequencies (for example, frequencies in the Ka-, Ku-,and/or Q-bands) and applying either right hand circular polarization orleft hand circular polarization. The resulting RF spot beam signals aretransmitted by the satellite-based RF communication system 164 asforward RF service links 176 via the spot beams 172 of the RF servicelinks 170 for receipt, demodulation, and decoding to retrieve the dataoriginally provided in the spot beam forward feeder link data streams tothe forward RF feeder link beam generators 510 of the HAP data center126.

The examples shown in FIGS. 5-7 illustrate essentially an “analogtransparent architecture” or “bent-pipe architecture,” in which themodulation and coding initially transmitted by the feeder RFT array 128in the forward direction, or initially transmitted by the end-usersatellite RFTs 112 in the reverse direction, is not changed by the HAP140 or the satellite 160. This allows for changes in modulation schemesto be employed in both the forward and reverse directions withoutchanges to the hardware of the HAP 140 or the satellite 160 and allowsthe HAP data center 126 to implement technologies such as ground-basedbeam forming or other precoding techniques.

However, regenerative retransmission techniques can be performed at theHAP and/or satellite, in which received signals are demodulated, errorcorrected, and remodulated (in some instances with a differentmodulation scheme than in the received signal). A drawback ofregenerative retransmission is a substantial power requirement atterabit per second data rates on platforms with limited power andalready substantial power requirements.

FIGS. 8-10 illustrate examples of station-keeping and handoveroperations performed among a plurality of HAPs being operated as part ofthe telecommunication system 100, as described for the HAP 140 in FIGS.1, 3, 5, and 6. Issues such as a leaking or torn envelope 142 orunscheduled repairs can unexpectedly take a currently operating HAP outof service with little to no notice. Additionally, HAPs may be returnedto earth periodically for routine maintenance and hardware or softwareupgrades.

In FIG. 8, a first HAP payload 144 and a second HAP payload 810 areoperating at approximately a first altitude 802 in proximity to thefeeder RFT array 128, with the first HAP payload 144 at a first zenithdistance θ_(804a) relative to the feeder RFT array 128, and the secondHAP payload 810 at a second zenith distance θ_(814a). The first HAPpayload 144 is operating RF service links 130 at their full capacity andoperating corresponding forward optical feeder link 152 and reverseoptical feeder link 154 with the satellite 160. To be prepared tohandover the operations of the first HAP payload 144 to the second HAPpayload 810, the optical feeder communication system of the second HAPpayload 810 is performing PAT of the satellite 160 by use of an opticalbeacon signal 830 transmitted by the satellite 160, and the RF feedercommunication system of the second HAP payload 810 is tracking thefeeder RFT array 128 via RF transmissions by one or more feeder RFTs 210included in the feeder RFT array 128. Additionally, via opticalcommunication terminals 822 and 824 in respective HAP payloads 144 and810, a bidirectional optical link is established and maintained betweenthe HAP payloads 144 and 810.

FIG. 9 illustrates an example in which a handover operation is performedfrom the first HAP payload 144 to the second HAP payload 810. In thisexample, the first HAP payload 144 is at an altitude 902 and anincreased horizontal distance 920 from the feeder RFT array 128, withthe first HAP payload 144 being at an increased third zenith distanceθ_(804b) relative to the feeder RFT array 128. The second HAP payload810 is at a fourth zenith distance θ_(814b) that allows it to operatethe RF feeder links 130 at their full capacity. Thus, a handoffoperation is performed from the first HAP payload 144 to the second HAPpayload 810, in which the feeder RFT array 128 establishes new RF feederlinks with the second HAP payload 810, and the second HAP payload 810operates the optical feeder links 152 and 154 with the satellite. Withthe second HAP payload 810 having made preparations to service as a “hotspare” as shown in FIG. 8, this handoff may be performed with verylittle interruption in service between the feeder RFT array 128 and thesatellite 160. The first HAP payload 144 may perform operations to beprepared as a “hot spare,” including performing PAT of the opticalbeacon 830, in the event that the first HAP payload 144 ends up in aposition suitable for that purpose. In some circumstances, a third HAPpayload 910 may be launched, whether in response to the handover, aprediction of the handover, or other considerations for operation of afleet of HAPs, to eventually operate as a “hot spare” as done by thesecond HAP payload 810 in FIG. 8.

FIG. 10 illustrates an example arrangement of the fleet of three HAPpayloads 144, 810, and 910 after FIG. 9. In FIG. 10, the first HAPpayload 144 is returning to the surface for maintenance and/orrefueling, and is no longer making efforts to operate as a “hot spare.”Additionally, the third HAP payload 910 has reached a position in whichit is able to operate as a “hot spare.” Accordingly, the second HAPpayload 810 and the third HAP payload 910 have effectively assumed theroles previously shown for the first HAP payload 144 and the second HAPpayload 810 respectively in FIG. 8.

FIGS. 11A-D illustrate examples in which the RF feeder links 130 areoperated with degradation in capacity in accordance with a zenithdistance and azimuth of the HAP 140 relative to the feeder RFT array128. Such graceful degradation in capacity may be useful incircumstances in which a HAP currently providing all, or a significantportion, of the capacity has moved away from the feeder RFT array 128,but there is not another HAP immediately available to fully handover to.In FIG. 11A, the HAP 140 is at a fifth zenith distance θ₁₁₁₀ similar tothe first zenith distance θ_(804a) shown for the first HAP payload 144in FIG. 8. FIG. 11A includes an azimuth indicator 1114 to moreconveniently illustrate a first azimuth θ₁₁₁₂ of the HAP 140 withrespect to the feeder RFT array 128 (which has the arrangement of 61feeder RFTs 210 illustrated in FIG. 2C). At the fifth zenith distanceθ₁₁₁₀, a small portion of the feeder RFTs 210 opposite the azimuthindicator 1114 are at too oblique of an angle from the viewpoint of theHAP 140 for that portion of feeder RFTs 210 to be operated without RFinterference between them. For example, at the fifth zenith distanceθ₁₁₁₀, if feeder RFTs 210 h and 210 i are both active, there will be anunacceptable amount of RF interference between their respective RFfeeder links, and if feeder RFTs 210 i and 210 j are both active, therewill be an unacceptable amount of RF interference between theirrespective feeder links. This will cause the signal-to-noise plusinterference ratio (SINR) to decrease for each of the forward andreverse RF feeder links for those feeder RFTs 210. In response to this,5 feeder RFTs 210 (including the feeder RFT 210 i) that were previouslyoperating RFT feeder links 130 are disabled or otherwise removed fromthe RFT feeder links 130 between the HAP 140 and the feeder RFT array128. As a result, RF interference between the active RF feeder links 130is avoided; for example, feeder RFTs 210 h and 210 j can both remainactive without interfering with each other.

In FIG. 11B, the HAP 140 has moved to a position with an increased sixthzenith distance θ₁₁₂₀, and in response a total of 13 of the feeder RFTs210 (including a feeder RFT 210 k) have been disabled to allow theirneighboring feeder RFTs to operate as RF feeder links 130 with the HAP140 without interference. In FIG. 11C, the HAP 140 has advanced toanother position to a further increased seventh zenith distance θ₁₁₃₀,and in response a total of 28 of the feeder RFTs 210 (including a feederRFT 210 m) have been disabled. At this point, the RF feeder links 130are performing at roughly half of their full capacity, depending on themargins offered by the full set of 61 feeder RFTs 210 (as this mayprovide excess capacity to absorb such degradation to a certain degree).In FIG. 11D, the HAP 140 as advanced to another position, with an eighthzenith distance θ₁₁₄₀ similar to the seventh zenith distance θ₁₁₃₀ inFIG. 11C, but at a much different second azimuth θ₁₁₄₂. Although a samenumber of feeder RFTs 210 are disabled (including a feeder RFT 210 n) asin FIG. 11C, the selection of the disabled RFTs 210 is responsive to thesecond azimuth θ₁₁₄₂.

In some implementations, the RF feeder links 130 are operated withdegradation in capacity in accordance with a zenith distance and azimuthof the HAP 140 relative to the feeder RFT array 128. For example, in analternative compact arrangement of the 61 feeder RFTs 210 shown in FIGS.2C and 11A-11D, with the RFT cells 212 for the 61 feeder RFTs (referredto as “central feeder RFTs”) arranged hexagonally, the feeder RFT array128 includes an additional 18 spare feeder RFTs positioned around theperiphery of the central feeder RFTs. When the HAP 140 is positioneddirectly above the feeder RFT array 128 with this alternative compactarrangement, the central feeder RFTs are in active operation, withrespective RF feeder links 130 established with the HAP 140, and thespare feeder RFTs are inactive. This arrangement of active and inactivecentral feeder RFTs and spare feeder RFTs may be used while the zenithdistance and azimuth of the HAP 140 does not result in an unacceptableamount of interference occurring between neighboring RFTs 210.

Continuing with the alternative compact arrangement of the central andspare feeder RFTs, with the HAP 140 at a ninth zenith distance similarto the fifth zenith distance θ₁₁₁₀ shown in FIG. 11A and at a thirdazimuth similar to the first azimuth θ₁₁₁₂ shown in FIG. 11A, much as inFIG. 11A, a small portion of the central feeder RFTs opposite the HAP140 are at too oblique of an angle from the viewpoint of the HAP 140 forthat portion of the central feeder RFTs to be operated without RFinterference between them. In response to this, 11 of the central feederRFTs, positioned to the right of a line are selectively deactivated, and11 (the same number, if available, and to the left of the line) of thespare feeder RFTs are selectively activated with respective RF feederlinks 130 operated with the HAP 140, with the remaining central feederRFTs remaining active and the remaining spare feeder RFTs remaininginactive. The arrangement of active and inactive central and spare RFTsis determined based on at least the ninth zenith distance and/or thethird azimuth of the HAP 140. Additionally, in response to a centralfeeder RFT being deactivated for maintenance or repair, a spare RFT maybe activated to maintain a total number of RF feeder links 130.

It is noted that although above FIGS. 11A-11D and the alternativecompact arrangement of the central and spare feeder RFTs are describedin terms of feeder RFTs 210 being in active or inactive states, otherchanges in operation of the feeder RFT array 128 and the RFT feederlinks 130 may be performed in response to changes in the zenith distanceand/or the azimuth of the HAP 140 with respect to the feeder RFT array128. Such changes may also involve the selection of feeder RFTs 128 inarrangements similar to those described for FIGS. 11A-11D and thealternative compact arrangement of the central and spare feeder RFTs.For example, encoding and/or modulation parameters may be changed toincrease the error protection on interfering RF feeder links. This willmaintain the error rate at an acceptable level at a cost of reducing theefficiency and data throughput of those RF feeder links. As the errorincreases, the total data throughput for the active RF feeder links 130may become unacceptably low (for example, falling below a thresholdvalue). In such cases, portions of the feeder RFTs 210 may beselectively deactivated and/or activated as described for 11A-11D andthe alternative compact arrangement of the central and spare feederRFTs. In part, these changes, and the changes described in FIGS. 11A-11Dand for the alternative compact arrangement of the central and sparefeeder RFTs, may be performed in response to closed loop signal qualitymonitoring.

FIGS. 12A and 12B show other approaches in which degraded capacity canbe provided between a HAP and the feeder RFT array 128, but in whichother HAPs pick up the remaining capacity. In FIG. 12A, there are firstand second HAPs 1210 at respective tenth and eleventh zenith distancesθ₁₂₁₂ and θ₁₂₂₂, which are both approximately the same as the fifthzenith distance θ₁₁₀₀ in FIG. 11A, and are at respective fourth andfifth azimuths θ₁₂₁₄ and θ₁₂₂₄ (with corresponding azimuth indicators1216 and 1226). The feeder RFTs 210 of the feeder RFT array 128 are allactive, with the telecommunication system 100 being configured toassociate each RF feeder link 130 with either the first HAP 1210 or thesecond HAP 1220 based on their respective tenth and eleventh zenithdistances θ₁₂₁₂ and θ₁₂₂₂ and their respective fourth and fifth azimuthsθ₁₂₁₄ and θ₁₂₂₄. In this example, 32 of the feeder RFTs 210 (including afeeder RFT 210 s) are linked with the first HAP 1210, and the remaining29 of the feeder RFTs 210 (including a feeder RFT 210 t) are linked withthe second HAP 1220. An optical link between the first and second HAPs1210 and 1220 may be used to relay feeder data between the two HAPs 1210and 1220 while operating only a single optical feeder link between asatellite and just one of the HAPs 1210 and 1220. With this arrangement,

FIG. 12B illustrates a similar example involving three HAPs 1230, 1240,and 1250 with active RF feeder links 130 with the feeder RFT array 128.In FIG. 12B, the three HAPs 1230, 1240, and 1250 are at respectivesixth, seventh, and eighth azimuths θ₁₂₃₄, θ₁₂₄₄, and θ₁₂₅₄ (withcorresponding azimuth indicators 1236, 1246, and 1256). The feeder RFTs210 of the feeder RFT array 128 are all active, with thetelecommunication system 100 being configured to associate each RFfeeder link 130 with one of the HAPs 1230, 1240, and 1250 based on theirrespective zenith distances (not shown in FIG. 12B) and their respectivesixth, seventh, and eighth azimuths θ₁₂₃₄, θ₁₂₄₄, and θ₁₂₅₄. In thisexample, 21 of the feeder RFTs 210 (including a feeder RFT 210 u) arelinked with the HAP 1230, 20 of the feeder RFTs 210 (including a feederRFT 210 v) are linked with the HAP 1240, and the remaining 20 of thefeeder RFTs 210 (including a feeder RFT 210 w) are linked with the HAP1250.

U.S. Pat. No. 6,327,063 (entitled “Reconfigurable Laser CommunicationsTerminal” and issued on Dec. 4, 2001), U.S. Pat. No. 9,723,386 (entitled“Communication Device” and issued on Aug. 1, 2017); and US PatentApplication Publication Numbers 2003/0213872 (entitled “High altitudeplatform control system” and published on Nov. 20, 2003), 2013/0177321(entitled “Balloon Network with Free-Space Optical Communication betweenSuper-Node Balloons and RF Communication between Super-Node and Sub-NodeBalloons” and published on Jul. 11, 2013), 2013/0177322 (entitled“Establishing Optical-Communication Lock with Nearby Balloon” andpublished on Jul. 11, 2013), 2013/0179008 (entitled “USING PREDICTEDMOVEMENT TO MAINTAIN OPTICAL-COMMUNICATION LOCK WITH NEARBY BALLOON” andpublished on Jul. 11, 2013), 2014/0085135 (entitled “Balloon-BasedPositioning System and Method” and published on Mar. 27, 2014),2015/0063159 (entitled “Re-tasking Balloons in a Balloon Network Basedon Expected Failure Modes of Balloons” and published on Mar. 5, 2015),2015/0244458 (entitled “OPTICAL COMMUNICATION TERMINAL” and published onAug. 27, 2015), 2015/0270890 (entitled “APPARATUS AND METHOD FOR NETWORKLEVEL SYNCHRONIZATION IN MULTIPLE LOW EARTH ORBIT (LEO) SATELLITECOMMUNICATIONS SYSTEMS” and published on Sep. 24, 2015), 2015/0271730(entitled “APPARATUS AND METHOD FOR EFFICIENT HANDOVER FOR LOW EARTHORBIT (LEO) SATELLITE SYSTEMS” and published on Sep. 24, 2015),2015/0318916 (entitled “SYSTEM AND ARCHITECTURE FOR SPACE-BASED ANDMOBILE TERRESTRIAL SENSOR VEHICLES, AND END-TO-END NETWORK FORAGGREGATION AND PROCESSING OF SENSOR DATA” and published on Nov. 5,2015), 2016/0037434 (entitled “CENTRALIZED GROUND-BASED ROUTEDETERMINATION AND TRAFFIC ENGINEERING FOR SOFTWARE DEFINED SATELLITECOMMUNICATIONS NETWORKS” and published on Feb. 4, 2016), 2016/0105806(entitled “MULTIBEAM COVERAGE FOR A HIGH ALTITUDE PLATFORM” andpublished on Apr. 14, 2016), 2016/0204865 (entitled “LINK ARCHITECTUREAND SPACECRAFT TERMINAL FOR HIGH RATE DIRECT TO EARTH OPTICALCOMMUNICATIONS” and published on Jul. 14, 2016), 2016/0211908 (entitled“HIGH ALTITUDE PLATFORM WITH MULTIBEAM COVERAGE FOR AERO-BASEDTERMINALS” and published on Jul. 21, 2016), 2017/0085411 (entitled“MODULATION AND CODING FOR A HIGH ALTITUDE PLATFORM” and published onMar. 23, 2017), 2017/0272131 (entitled “Interference Mitigation Systemsin High Altitude Platform Overlaid With a Terrestrial Network” andpublished on Sep. 21, 2017), 2017/0294957 (entitled “HYBRID SATELLITESYSTEMS FOR ENHANCED PERFORMANCE AND ENHANCED QUALITY OF SERVICEBROADBAND COMMUNICATIONS” and published on Oct. 12, 2017), 2018/0074208(entitled “SYSTEM AND METHOD FOR EFFICIENT BROADCAST OF SATELLITECONSTELLATION EPHEMERIS INFORMATION” and published on Mar. 15, 2018),2018/0084476 (entitled “RADIO RESOURCE MANAGEMENT AND ROUTING FOR FIXEDDATA CIRCUITS IN AN NGSO SATELLITE DATA COMMUNICATIONS SYSTEM” andpublished on Mar. 22, 2018), 2018/0098247 (entitled “MULTI-MODEM USERTERMINAL AND POLICY-BASED MANAGEMENT FOR SATELLITE TRANSPORT RESILIENCY”and published on Apr. 5, 2018), 2018/0160373 (entitled “METHODS FORUPLINK POWER CONTROL TO COMBAT RAIN FADE IN WIDEBAND SATELLITE SYSTEMS”and published on Jun. 7, 2018), 2018/0191431 (entitled “EFFICIENTAUTOMATIC REPEAT REQUEST FOR FREE SPACE OPTICAL COMMUNICATION” andpublished on Jul. 5, 2018), and 2018/0192298 (entitled “METHOD ANDSYSTEM FOR ORIENTING A PHASED ARRAY ANTENNA” and published on Jul. 2,2018), 2018/0234284 (entitled “MODULATION AND CODING FOR A HIGH ALTITUDEPLATFORM” and published on Aug. 16, 2018), each of which areincorporated by reference herein in their entireties.

The detailed examples of systems, devices, and techniques described inconnection with FIGS. 1-12B are presented herein for illustration of thedisclosure and its benefits. Such examples of use should not beconstrued to be limitations on the logical process implementations ofthe disclosure, nor should variations of user interface methods fromthose described herein be considered outside the scope of the presentdisclosure. In some implementations, various features described in FIGS.1-12B are implemented in respective modules, which may also be referredto as, and/or include, logic, components, units, and/or mechanisms.Modules may constitute either software modules (for example, codeembodied on a machine-readable medium) or hardware modules.

In some examples, a hardware module may be implemented mechanically,electronically, or with any suitable combination thereof. For example, ahardware module may include dedicated circuitry or logic that isconfigured to perform certain operations. For example, a hardware modulemay include a special-purpose processor, such as a field-programmablegate array (FPGA) or an Application Specific Integrated Circuit (ASIC).A hardware module may also include programmable logic or circuitry thatis temporarily configured by software to perform certain operations, andmay include a portion of machine-readable medium data and/orinstructions for such configuration. For example, a hardware module mayinclude software encompassed within a programmable processor configuredto execute a set of software instructions. It will be appreciated thatthe decision to implement a hardware module mechanically, in dedicatedand permanently configured circuitry, or in temporarily configuredcircuitry (for example, configured by software) may be driven by cost,time, support, and engineering considerations.

Accordingly, the phrase “hardware module” should be understood toencompass a tangible entity capable of performing certain operations andmay be configured or arranged in a certain physical manner, be that anentity that is physically constructed, permanently configured (forexample, hardwired), and/or temporarily configured (for example,programmed) to operate in a certain manner or to perform certainoperations described herein. As used herein, “hardware-implementedmodule” refers to a hardware module. Considering examples in whichhardware modules are temporarily configured (for example, programmed),each of the hardware modules need not be configured or instantiated atany one instance in time. For example, where a hardware module includesa programmable processor configured by software to become aspecial-purpose processor, the programmable processor may be configuredas respectively different special-purpose processors (for example,including different hardware modules) at different times. Software mayaccordingly configure a particular processor or processors, for example,to constitute a particular hardware module at one instance of time andto constitute a different hardware module at a different instance oftime. A hardware module implemented using one or more processors may bereferred to as being “processor implemented” or “computer implemented.”

Hardware modules can provide information to, and receive informationfrom, other hardware modules. Accordingly, the described hardwaremodules may be regarded as being communicatively coupled. Where multiplehardware modules exist contemporaneously, communications may be achievedthrough signal transmission (for example, over appropriate circuits andbuses) between or among two or more of the hardware modules. Inimplementations in which multiple hardware modules are configured orinstantiated at different times, communications between such hardwaremodules may be achieved, for example, through the storage and retrievalof information in memory devices to which the multiple hardware moduleshave access. For example, one hardware module may perform an operationand store the output in a memory device, and another hardware module maythen access the memory device to retrieve and process the stored output.

In some examples, at least some of the operations of a method may beperformed by one or more processors or processor-implemented modules.Moreover, the one or more processors may also operate to supportperformance of the relevant operations in a “cloud computing”environment or as a “software as a service” (SaaS). For example, atleast some of the operations may be performed by, and/or among, multiplecomputers (as examples of machines including processors), with theseoperations being accessible via a communication network (for example,the Internet) and/or via one or more software interfaces (for example,an application program interface (API)). The performance of certain ofthe operations may be distributed among the processors, not onlyresiding within a single machine, but deployed across a number ofmachines. Processors or processor-implemented modules may be located ina single geographic location (for example, within a home or officeenvironment, or a server farm), or may be distributed across multiplegeographic locations.

FIG. 13 is a block diagram 1300 illustrating an example softwarearchitecture 1302, various portions of which may be used in conjunctionwith various hardware architectures herein described, which mayimplement any of the above-described features. FIG. 13 is a non-limitingexample of a software architecture and it will be appreciated that manyother architectures may be implemented to facilitate the functionalitydescribed herein. A representative hardware layer 1304 includes aprocessing unit 1306 and associated executable instructions 1308. Theexecutable instructions 1308 represent executable instructions of thesoftware architecture 1302, including implementation of the methods,modules and so forth described herein. The hardware layer 1304 alsoincludes a memory/storage 1310, which also includes the executableinstructions 1308 and accompanying data. The hardware layer 1304 mayalso include other hardware modules 1312. Instructions 1308 held byprocessing unit 1308 may be portions of instructions 1308 held by thememory/storage 1310.

The example software architecture 1302 may be conceptualized as layers,each providing various functionality. For example, the softwarearchitecture 1302 may include layers and components such as an operatingsystem (OS) 1314, libraries 1316, frameworks 1318, applications 1320,and a presentation layer 1324. Operationally, the applications 1320and/or other components within the layers may invoke API calls 1324 toother layers and receive corresponding results 1326. The layersillustrated are representative in nature and other softwarearchitectures may include additional or different layers. For example,some mobile or special purpose operating systems may not provide theframeworks/middleware 1318.

The OS 1314 may manage hardware resources and provide common services.The OS 1314 may include, for example, a kernel 1328, services 1330, anddrivers 1332. The kernel 1328 may act as an abstraction layer betweenthe hardware layer 1304 and other software layers. For example, thekernel 1328 may be responsible for memory management, processormanagement (for example, scheduling), component management, networking,security settings, and so on. The services 1330 may provide other commonservices for the other software layers. The drivers 1332 may beresponsible for controlling or interfacing with the underlying hardwarelayer 1304. For instance, the drivers 1332 may include display drivers,camera drivers, memory/storage drivers, peripheral device drivers (forexample, via Universal Serial Bus (USB)), network and/or wirelesscommunication drivers, audio drivers, and so forth depending on thehardware and/or software configuration.

The libraries 1316 may provide a common infrastructure that may be usedby the applications 1320 and/or other components and/or layers. Thelibraries 1316 typically provide functionality for use by other softwaremodules to perform tasks, rather than rather than interacting directlywith the OS 1314. The libraries 1316 may include system libraries 1334(for example, C standard library) that may provide functions such asmemory allocation, string manipulation, file operations. In addition,the libraries 1316 may include API libraries 1336 such as medialibraries (for example, supporting presentation and manipulation ofimage, sound, and/or video data formats), graphics libraries (forexample, an OpenGL library for rendering 2D and 3D graphics on adisplay), database libraries (for example, SQLite or other relationaldatabase functions), and web libraries (for example, WebKit that mayprovide web browsing functionality). The libraries 1316 may also includea wide variety of other libraries 1338 to provide many functions forapplications 1320 and other software modules.

The frameworks 1318 (also sometimes referred to as middleware) provide ahigher-level common infrastructure that may be used by the applications1320 and/or other software modules. For example, the frameworks 1318 mayprovide various graphic user interface (GUI) functions, high-levelresource management, or high-level location services. The frameworks1318 may provide a broad spectrum of other APIs for applications 1320and/or other software modules.

The applications 1320 include built-in applications 1320 and/orthird-party applications 1322. Examples of built-in applications 1320may include, but are not limited to, a contacts application, a browserapplication, a location application, a media application, a messagingapplication, and/or a game application. Third-party applications 1322may include any applications developed by an entity other than thevendor of the particular platform. The applications 1320 may usefunctions available via OS 1314, libraries 1316, frameworks 1318, andpresentation layer 1324 to create user interfaces to interact withusers.

Some software architectures use virtual machines, as illustrated by avirtual machine 1328. The virtual machine 1328 provides an executionenvironment where applications/modules can execute as if they wereexecuting on a hardware machine (such as the machine 1400 of FIG. 14,for example). The virtual machine 1328 may be hosted by a host OS (forexample, OS 1314) or hypervisor, and may have a virtual machine monitor1326 which manages operation of the virtual machine 1328 andinteroperation with the host operating system. A software architecture,which may be different from software architecture 1302 outside of thevirtual machine, executes within the virtual machine 1328 such as an OS1350, libraries 1352, frameworks 1354, applications 1356, and/or apresentation layer 1358.

FIG. 14 is a block diagram illustrating components of an example machine1400 configured to read instructions from a machine-readable medium (forexample, a machine-readable storage medium) and perform any of thefeatures described herein. The example machine 1400 is in a form of acomputer system, within which instructions 1416 (for example, in theform of software components) for causing the machine 1400 to perform anyof the features described herein may be executed. As such, theinstructions 1416 may be used to implement modules or componentsdescribed herein. The instructions 1416 cause unprogrammed and/orunconfigured machine 1400 to operate as a particular machine configuredto carry out the described features. The machine 1400 may be configuredto operate as a standalone device or may be coupled (for example,networked) to other machines. In a networked deployment, the machine1400 may operate in the capacity of a server machine or a client machinein a server-client network environment, or as a node in a peer-to-peeror distributed network environment. Machine 1400 may be embodied as, forexample, a server computer, a client computer, a personal computer (PC),a tablet computer, a laptop computer, a netbook, a set-top box (STB), agaming and/or entertainment system, a smart phone, a mobile device, awearable device (for example, a smart watch), and an Internet of Things(IoT) device. Further, although only a single machine 1400 isillustrated, the term “machine” include a collection of machines thatindividually or jointly execute the instructions 1416.

The machine 1400 may include processors 1410, memory 1430, and I/Ocomponents 1450, which may be communicatively coupled via, for example,a bus 1402. The bus 1402 may include multiple buses coupling variouselements of machine 1400 via various bus technologies and protocols. Inan example, the processors 1410 (including, for example, a centralprocessing unit (CPU), a graphics processing unit (GPU), a digitalsignal processor (DSP), an ASIC, or a suitable combination thereof) mayinclude one or more processors 1412 a to 1412 n that may execute theinstructions 1416 and process data. In some examples, one or moreprocessors 1410 may execute instructions provided or identified by oneor more other processors 1410. The term “processor” includes amulti-core processor including cores that may execute instructionscontemporaneously. Although FIG. 14 shows multiple processors, themachine 1400 may include a single processor with a single core, a singleprocessor with multiple cores (for example, a multi-core processor),multiple processors each with a single core, multiple processors eachwith multiple cores, or any combination thereof. In some examples, themachine 1400 may include multiple processors distributed among multiplemachines.

The memory/storage 1430 may include a main memory 1432, a static memory1434, or other memory, and a storage unit 1436, both accessible to theprocessors 1410 such as via the bus 1402. The storage unit 1436 andmemory 1432, 1434 store instructions 1416 embodying any one or more ofthe functions described herein. The memory/storage 1430 may also storetemporary, intermediate, and/or long-term data for processors 1410. Theinstructions 1416 may also reside, completely or partially, within thememory 1432, 1434, within the storage unit 1436, within at least one ofthe processors 1410 (for example, within a command buffer or cachememory), within memory at least one of I/O components 1450, or anysuitable combination thereof, during execution thereof. Accordingly, thememory 1432, 1434, the storage unit 1436, memory in processors 1410, andmemory in I/O components 1450 are examples of machine-readable media.

As used herein, “machine-readable medium” refers to a device able totemporarily or permanently store instructions and data that causemachine 1400 to operate in a specific fashion. The term“machine-readable medium,” as used herein, does not encompass transitoryelectrical or electromagnetic signals per se (such as on a carrier wavepropagating through a medium); the term “machine-readable medium” maytherefore be considered tangible and non-transitory. Non-limitingexamples of a non-transitory, tangible machine-readable medium mayinclude, but are not limited to, nonvolatile memory (such as flashmemory or read-only memory (ROM)), volatile memory (such as a staticrandom-access memory (RAM) or a dynamic RAM), buffer memory, cachememory, optical storage media, magnetic storage media and devices,network-accessible or cloud storage, other types of storage, and/or anysuitable combination thereof. The term “machine-readable medium” appliesto a single medium, or combination of multiple media, used to storeinstructions (for example, instructions 1416) for execution by a machine1400 such that the instructions, when executed by one or more processors1410 of the machine 1400, cause the machine 1400 to perform and one ormore of the features described herein. Accordingly, a “machine-readablemedium” may refer to a single storage device, as well as “cloud-based”storage systems or storage networks that include multiple storageapparatus or devices.

The I/O components 1450 may include a wide variety of hardwarecomponents adapted to receive input, provide output, produce output,transmit information, exchange information, capture measurements, and soon. The specific I/O components 1450 included in a particular machinewill depend on the type and/or function of the machine. For example,mobile devices such as mobile phones may include a touch input device,whereas a headless server or IoT device may not include such a touchinput device. The particular examples of I/O components illustrated inFIG. 14 are in no way limiting, and other types of components may beincluded in machine 1400. The grouping of I/O components 1450 are merelyfor simplifying this discussion, and the grouping is in no way limiting.In various examples, the I/O components 1450 may include user outputcomponents 1452 and user input components 1454. User output components1452 may include, for example, display components for displayinginformation (for example, a liquid crystal display (LCD) or aprojector), acoustic components (for example, speakers), hapticcomponents (for example, a vibratory motor or force-feedback device),and/or other signal generators. User input components 1454 may include,for example, alphanumeric input components (for example, a keyboard or atouch screen), pointing components (for example, a mouse device, atouchpad, or another pointing instrument), and/or tactile inputcomponents (for example, a physical button or a touch screen thatprovides location and/or force of touches or touch gestures) configuredfor receiving various user inputs, such as user commands and/orselections.

In some examples, the I/O components 1450 may include biometriccomponents 1456 and/or position components 1462, among a wide array ofother environmental sensor components. The biometric components 1456 mayinclude, for example, components to detect body expressions (forexample, facial expressions, vocal expressions, hand or body gestures,or eye tracking), measure biosignals (for example, heart rate or brainwaves), and identify a person (for example, via voice-, retina-, and/orfacial-based identification). The position components 1462 may include,for example, location sensors (for example, a Global Position System(GPS) receiver), altitude sensors (for example, an air pressure sensorfrom which altitude may be derived), and/or orientation sensors (forexample, magnetometers).

The I/O components 1450 may include communication components 1464,implementing a wide variety of technologies operable to couple themachine 1400 to network(s) 1470 and/or device(s) 1480 via respectivecommunicative couplings 1472 and 1482. The communication components 1464may include one or more network interface components or other suitabledevices to interface with the network(s) 1470. The communicationcomponents 1464 may include, for example, components adapted to providewired communication, wireless communication, cellular communication,Near Field Communication (NFC), Bluetooth communication, Wi-Fi, and/orcommunication via other modalities. The device(s) 1480 may include othermachines or various peripheral devices (for example, coupled via USB).

In some examples, the communication components 1464 may detectidentifiers or include components adapted to detect identifiers. Forexample, the communication components 1464 may include Radio FrequencyIdentification (RFID) tag readers, NFC detectors, optical sensors (forexample, one- or multi-dimensional bar codes, or other optical codes),and/or acoustic detectors (for example, microphones to identify taggedaudio signals). In some examples, location information may be determinedbased on information from the communication components 1462, such as,but not limited to, geo-location via Internet Protocol (IP) address,location via Wi-Fi, cellular, NFC, Bluetooth, or other wireless stationidentification and/or signal triangulation.

While various embodiments have been described, the description isintended to be exemplary, rather than limiting, and it is understoodthat many more embodiments and implementations are possible that arewithin the scope of the embodiments. Although many possible combinationsof features are shown in the accompanying figures and discussed in thisdetailed description, many other combinations of the disclosed featuresare possible. Any feature of any embodiment may be used in combinationwith or substituted for any other feature or element in any otherembodiment unless specifically restricted. Therefore, it will beunderstood that any of the features shown and/or discussed in thepresent disclosure may be implemented together in any suitablecombination. Accordingly, the embodiments are not to be restrictedexcept in light of the attached claims and their equivalents. Also,various modifications and changes may be made within the scope of theattached claims.

While the foregoing has described what are considered to be the bestmode and/or other examples, it is understood that various modificationsmay be made therein and that the subject matter disclosed herein may beimplemented in various forms and examples, and that the teachings may beapplied in numerous applications, only some of which have been describedherein. It is intended by the following claims to claim any and allapplications, modifications and variations that fall within the truescope of the present teachings.

Unless otherwise stated, all measurements, values, ratings, positions,magnitudes, sizes, and other specifications that are set forth in thisspecification, including in the claims that follow, are approximate, notexact. They are intended to have a reasonable range that is consistentwith the functions to which they relate and with what is customary inthe art to which they pertain.

The scope of protection is limited solely by the claims that now follow.That scope is intended and should be interpreted to be as broad as isconsistent with the ordinary meaning of the language that is used in theclaims when interpreted in light of this specification and theprosecution history that follows and to encompass all structural andfunctional equivalents. Notwithstanding, none of the claims are intendedto embrace subject matter that fails to satisfy the requirement ofSections 101, 102, or 103 of the Patent Act, nor should they beinterpreted in such a way. Any unintended embracement of such subjectmatter is hereby disclaimed.

Except as stated immediately above, nothing that has been stated orillustrated is intended or should be interpreted to cause a dedicationof any component, step, feature, object, benefit, advantage, orequivalent to the public, regardless of whether it is or is not recitedin the claims.

It will be understood that the terms and expressions used herein havethe ordinary meaning as is accorded to such terms and expressions withrespect to their corresponding respective areas of inquiry and studyexcept where specific meanings have otherwise been set forth herein.Relational terms such as first and second and the like may be usedsolely to distinguish one entity or action from another withoutnecessarily requiring or implying any actual such relationship or orderbetween such entities or actions. The terms “comprises,” “comprising,”or any other variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to suchprocess, method, article, or apparatus. An element proceeded by “a” or“an” does not, without further constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises the element.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various examples for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claims require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed example. Thus, the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separately claimed subject matter.

What is claimed is:
 1. A telecommunication system comprising: a singlegeostationary earth orbiting satellite including: a first opticalcommunication system configured to receive forward-direction user datavia a forward optical link, and a first radio frequency (RF)communication system configured to transmit, via a plurality of RF spotbeams, the forward-direction user data received via the forward opticallink; a single stratospheric high-altitude communication deviceincluding: a second RF communication system configured to receive theforward-direction user data via a plurality of concurrent forward RFfeeder links, and a second optical communication system configured totransmit via the forward optical link the forward-direction user datareceived via the plurality of forward RF feeder links; and aground-based feeder RF terminal (RFT) array including a plurality ofground-based feeder RF terminals (RFTs) configured to transmit arespective one of the plurality of forward RF feeder links andpositioned at a same RF feeder site, wherein a substantial portion offorward feeder data throughput for all forward RF service linktransmissions by the satellite is carried via the forward optical linkand the plurality of forward RF feeder links.
 2. The telecommunicationsystem of claim 1, further comprising a data center configured to, foreach feeder RFT of the feeder RFTs: receive a respective portion of theforward-direction user data as network data for delivery to thesatellite; encode the network data in a first forward RF feeder linksignal; and transmit the first forward RF feeder link signal to thehigh-altitude communication device as a respective one of the pluralityof forward RF feeder links via the feeder RFT.
 3. The telecommunicationsystem of claim 1, wherein: the plurality of RF spot beams includes afirst RF spot beam and a second RF spot beam; and the geostationaryearth orbiting satellite is configured to: demultiplex the receivedforward optical link into a plurality of optical channel signals withdifferent wavelengths, the plurality of optical channel signalsincluding a first optical channel signal, obtain a first intermediateforward RF signal by an optical to electrical conversion of the firstoptical channel signal, demultiplex the first intermediate forward RFsignal into a plurality of RF subband signals, the plurality of RFsubband signals including a first RF subband signal and a second RFsubband signal, generate a first forward RF service link signal byupconverting and amplifying the first RF subband signal, transmit thefirst forward RF service link signal via the first RF spot beam,generate a second RF service link signal by upconverting and amplifyingthe second RF subband signal, and transmit the second RF service linksignal via the second RF spot beam.
 4. The telecommunication system ofclaim 3, wherein: the plurality of forward RF feeder links includes afirst forward RF feeder link and a second forward RF feeder link; andthe high-altitude communication device is configured to: downconvert thefirst forward RF feeder link to a lower RF band to obtain a firstdownconverted RF signal, downconvert the second forward RF feeder linkto a lower RF band to obtain a second downconverted RF signal, modulatethe first downconverted RF signal onto a first laser beam with a firstoptical wavelength, modulate the second downconverted RF signal onto asecond laser beam with a second optical wavelength that is differentthan the first optical wavelength, and multiplex the modulated firstlaser beam and the modulated second laser beam into the forward opticallink.
 5. The telecommunication system of claim 1, wherein: the first RFcommunication system is further configured to receive reverse-directionuser data via a plurality of reverse RF service links including a firstreverse RF service link received via a first RF spot beam and a secondRF service link received via a second RF spot beam; the first opticalcommunication system is further configured to transmit via a reverseoptical link the reverse-direction user data received via the pluralityof reverse RF service links; the second optical communication system isfurther configured to receive the reverse-direction user data via thereverse optical link; and the second RF communication system is furtheradapted to transmit, via a plurality of reverse RF feeder links to thefeeder RFT array, the reverse-direction user data received via thereverse optical link.
 6. The telecommunication system of claim 5,further comprising a data center configured to, for each feeder RFT ofthe feeder RFTs: receive a respective first reverse RF feeder linkincluded in the plurality of reverse RF feeder links; decode arespective first portion of the reverse-direction user data from thereceived first reverse RF feeder link; and transmit the first portion ofthe reverse-direction user data as network data received via thesatellite.
 7. The telecommunication system of claim 5, wherein thesatellite is configured to: multiplex the first and second reverse RFservice links in respective subbands of an intermediate reverse RFfeeder link signal; modulate the intermediate reverse RF feeder linksignal onto a first laser beam with a first optical wavelength; andmultiplex the modulated first laser beam into the reverse optical link.8. The telecommunication system of claim 5, wherein the satellite isfurther configured to: multiplex the first and second reverse RF servicelinks in respective subbands of an intermediate reverse RF feeder linksignal; modulate the intermediate reverse RF feeder link signal onto afirst laser beam with a first optical wavelength; and multiplex themodulated first laser beam into the reverse optical link.
 9. Thetelecommunication system of claim 7, wherein: the plurality of reverseRF feeder links includes a first reverse RF feeder link and a secondreverse RF feeder link; and the high-altitude communication device isconfigured to: demultiplex the received reverse optical link into aplurality of optical channel signals with different wavelengths, theplurality of optical channel signals including a first optical channelsignal and a second optical channel signal, obtain a first reverse RFsignal by an optical to electrical conversion of the first opticalchannel signal, obtain a second reverse RF signal by an optical toelectrical conversion of the second optical channel signal, generate thefirst reverse RF feeder link by upconverting and amplifying the firstreverse RF signal, and generate the second reverse RF feeder link signalby upconverting and amplifying the second reverse RF signal.
 10. Thetelecommunication system of claim 8, wherein: the plurality of forwardRF feeder links includes a first forward RF feeder link and a secondforward RF feeder link; the plurality of reverse RF feeder linksincludes a first reverse RF feeder link and a second reverse RF feederlink; and the high-altitude communication device is configured to:downconvert the first forward RF feeder link to a lower RF band toobtain a first downconverted RF signal, downconvert the second forwardRF feeder link to a lower RF band to obtain a second downconverted RFsignal, modulate the first downconverted RF signal onto a first laserbeam with a first optical wavelength, modulate the second downconvertedRF signal onto a second laser beam with a second optical wavelength thatis different than the first optical wavelength, multiplex the modulatedfirst laser beam and the modulated second laser beam into the forwardoptical link, demultiplex the received reverse optical link into aplurality of optical channel signals with different wavelengths, theplurality of optical channel signals including a first optical channelsignal and a second optical channel signal, obtain a first reverse RFsignal by an optical to electrical conversion of the first opticalchannel signal, obtain a second reverse RF signal by an optical toelectrical conversion of the second optical channel signal, generate thefirst reverse RF feeder link by upconverting and amplifying the firstreverse RF signal, and generate the second reverse RF feeder link signalby upconverting and amplifying the second reverse RF signal.
 11. Thetelecommunication system of claim 1, wherein the plurality ofground-based feeder RFTs are all positioned within a diameter of lessthan 1800 meters.
 12. The telecommunication system of claim 11, whereinthe plurality of ground-based feeder RFTs are all positioned within adiameter of less than 800 meters.
 13. The telecommunication system ofclaim 11, wherein the plurality of ground-based feeder RFTs includes atleast 40 ground-based feeder RFTs.
 14. The telecommunication system ofclaim 1, wherein the forward optical link has a total data throughput ofat least 1 terabit per second.
 15. The telecommunication system of claim1, wherein the stratospheric high-altitude communication device furtherincludes: a plurality of sensors; and a pointing, acquisition, andtracking (PAT) controller configured to perform, based on at leastsensor data obtained from the sensors, optical pointing of the forwardoptical link signal between the stratospheric high-altitudecommunication device and the satellite.
 16. A method of datatransmission, the method comprising: receiving, at a geostationary earthorbiting satellite, forward-direction user data via a forward opticallink; transmitting, by the geostationary earth orbiting satellite via aplurality of radio frequency (RF) spot beams, the forward-direction userdata received via the forward optical link; receiving, at astratospheric high-altitude communication device, forward-direction userdata via a plurality of concurrent forward RF feeder links;transmitting, by the stratospheric high-altitude communication devicevia the forward optical link, the forward-direction user data receivedvia the plurality of forward RF feeder links; transmitting, by each of aplurality of ground-based feeder RF terminals (RFTs) of an RFT array ata same RF feeder site, a respective one of the plurality of forward RFfeeder links, wherein a substantial portion of forward feeder datathroughput for all forward RF service link transmissions by thesatellite is carried via the forward optical link and the plurality offorward RF feeder links.
 17. The method of claim 16, further comprising:receiving, at the geostationary earth orbiting satellite,reverse-direction user data via a plurality of reverse RF service linksincluding a first reverse RF service link received via a first RF spotbeam and a second RF service link received via a second RF spot beam;transmitting, by the geostationary earth orbiting satellite via areverse optical link, the reverse-direction user data received via theplurality of reverse RF service links; receiving, at the stratospherichigh-altitude communication device, the reverse-direction user data viathe reverse optical link; and transmitting, by the stratospherichigh-altitude communication device via a plurality of reverse RF feederlinks to the feeder RFT array, the reverse-direction user data receivedvia the reverse optical link.
 18. The method of claim 16, wherein: theplurality of RF spot beams includes a first RF spot beam and a second RFspot beam; and the method further comprises: demultiplexing the receivedforward optical link into a plurality of optical channel signals withdifferent wavelengths, the plurality of optical channel signalsincluding a first optical channel signal, obtaining a first intermediateforward RF signal by an optical to electrical conversion of the firstoptical channel signal, demultiplexing the first intermediate forward RFsignal into a plurality of RF subband signals, the plurality of RFsubband signals including a first RF subband signal and a second RFsubband signal, generating a first forward RF service link signal byupconverting and amplifying the first RF subband signal, transmittingthe first forward RF service link signal via the first RF spot beam,generating a second RF service downlink signal by upconverting andamplifying the second RF subband signal, and transmitting the second RFservice downlink signal via the second RF spot beam.
 19. The method ofclaim 16, wherein the plurality of ground-based feeder RFTs are allpositioned within a diameter of less than 1800 meters.
 20. The method ofclaim 19, wherein the plurality of ground-based feeder RFTs includes atleast 40 ground-based feeder RFTs.
 21. The telecommunication system ofclaim 1, wherein the substantial portion of the forward feeder datathroughput comprises at least 95% of the forward feeder data throughput.22. The method of claim 16, wherein the substantial portion of theforward feeder data throughput comprises at least 95% of the forwardfeeder data throughput.
 23. A telecommunication system comprising: asingle geostationary earth orbiting satellite including: a first opticalcommunication system configured to receive forward-direction user datavia a forward optical link, and a first radio frequency (RF)communication system configured to transmit, via a plurality of RF spotbeams, the forward-direction user data received via the forward opticallink; a single stratospheric high-altitude communication deviceincluding: a second RF communication system configured to receive theforward-direction user data via a plurality of concurrent forward RFfeeder links, and a second optical communication system configured totransmit via the forward optical link the forward-direction user datareceived via the plurality of forward RF feeder links; and aground-based feeder RF terminal (RFT) array including a plurality ofground-based feeder RF terminals (RFTs) configured to transmit arespective one of the plurality of forward RF feeder links andpositioned at a same RF feeder site, wherein at least 95% of forwardfeeder data throughput for all forward RF service link transmissions bythe satellite is carried via the forward optical link and the pluralityof forward RF feeder links.